[P031] “ESO update and progress towards full membership” – Sarah Brough
I will provide an overview and update for Australia’s strategic partnership with ESO and a progress report on developing the case for full Australian membership. I will cover usage of ESO facilities by Australian astronomers, new instrumentation programs (especially those with Australian involvement), and other new opportunities. I will also discuss the Widefield Spectroscopic Telescope (WST) and Australia’s involvement in a proposed concept study for this potential post-ELT ESO facility.
[P079] “The Future of Observational Astronomers a survey on occupational identity in astronomy” – Hugo Walsh
Observational astronomy is a field where the ability to visually inspect images to find features of interest has traditionally been crucial to an astronomer’s success. The increase in the quantity of data collection in astronomy has necessitated the integration of automation in what were traditionally human-centred activities. The impact of automation on astronomical research has already been profound, enabling tasks and analyses that were previously impractical or impossible. Yet, despite these advancements, the astronomy community has not fully addressed the evolving role of astronomers as observers, nor have we extensively discussed the implications of increased automation on our professional identity. In 2023 we conducted one of the largest international surveys investigating occupational identity in observational astronomy. We received over 470 responses including 69 from astronomers from Australia and New Zealand. The goal of this survey was to better understand: (1) observational astronomers current and expected future interactions with automated processes, and (2) the extent to which physical presence at observatories is part of the research process within observational astronomy both now and in the future. Additional themes within the survey included the extent of automation used, the specific telescopes utilized, and crucially, the respondents’ sentiments about the evolving landscape of observational astronomy. Over 150 respondents provided insights into what factors influenced their happiness within the field. As automation continues to transform observational astronomy, it is essential for our community to engage in discussions about our evolving roles, the integration of automation, and how these changes influence our occupational identity.
[P077] “SKAO Science Operations update: a ‘year in the life’ of the world’s largest radio telescope” – Jess Broderick
The Square Kilometre Array Observatory (SKAO) Science Operations Team is focused on the development and implementation of various workflows and procedures to ensure that SKA-Low and SKA-Mid will be operationally ready for transformational science. In this talk, I will give an overview of who we are and our current key objectives. In particular, I will focus on progress for envisioning a ‘year in the life’ of both SKA-Low and SKA-Mid, including a range of science projects that could be scheduled as well as the associated data products and computational requirements. Efficient observational and data commensality will be crucial to the success of the telescope. We will seek community feedback as we refine our year in the life operational model, and I will outline how you can get involved so that we can best capture your scientific requirements.
[P120] “The DESI 2024 Cosmological Constraints” – Cullan Howlett
In April 2024, the Dark Energy Spectroscopic Instrument (DESI) collaboration released ground-breaking cosmological constraints using its first year of survey data. Combining redshifts from over 6 million galaxies, the largest such sample ever accumulated, DESI’s seven distinct measurements of the Baryon Acoustic Oscillation signal between 0.1 < z < 4.2 provide the most precise determination of the expansion history of our Universe to date.
Analysis of this data in combination with priors from Big-Bang Nucleosynthesis demonstrate general consistency with the flat LCDM cosmological model, with a Hubble Constant H0 = 68.52 +/- 0.62 km/s/Mpc. This measurement, independent of the Planck Cosmic Microwave Background (CMB) data, favours a lower value for the present-day expansion rate of the Universe.
However, beyond LCDM, the combination of DESI with CMB and Type-Ia supernovae data provides the most exquisite test of extended cosmological models to date --- and the surprising and exciting hint of a detection of time-varying Dark Energy. We find moderate preference for results that are discrepant with the LCDM model at between 2.5 – 3.9 sigma.
As such, this talk will present a summary of DESI’s new data, how this was analysed to obtain measurements of the expansion history (including our blinding methodology to mitigate against confirmation bias), and the potentially profound cosmological implications for these results. It will conclude with a discussion of what’s next for DESI, including even tighter constraints expected in 2024 from analysis of the ‘full shape’ of the galaxy clustering, as well as plans for the Year 3 dataset.
[P004] “Unveiling the Cosmic Dawn: Insights from Semi-Analytic Galaxy Formation Framework” – Yuxiang Qin
Understanding the evolution of galaxies over cosmic time and their influence on the surrounding intergalactic medium is crucial in cosmology. Cosmological simulations have emerged as indispensable tools in this pursuit. In this presentation, I will present a semi-analytic framework for galaxy formation, where sub-grid baryonic physics is directly applied to the histories of dark matter halos to derive galaxy properties.
By comparing these semi-analytic models to more detailed hydrodynamic simulations, where baryonic particles co-evolve with dark matter, I will reveal potential systematic biases in current models, particularly when studying low-mass galaxies formed during the Epoch ofReionization(EoR). As part of our endeavour to model faint galaxies potentially responsible for drivingreionization, I will discuss our latest endeavours. Specifically, I will highlight the inclusion of a distinct population of galaxies hosting metal-free stars and illustrate some of the unique characteristics of these earliest astronomical objects.
Finally, I will offer insights into how upcoming21-cmexperiments from the Square Kilometre Array may provide a ground-breaking opportunity to detect the signature of the first galaxies formed at the cosmic dawn, opening new avenues for understanding the early universe.
[P169] “Cosmology with GLEAM-X” – Brandon Venville [R]
One method of measuring the large-scale distribution of matter in the Universe is the angular correlation function (ACF). The ACF, for each angular scale, measures the counts of galaxy pairs when compared to that expected from a random distribution. The ACF can be predicted from structure formation theory, and used to make statistical inferences about the values of the cosmological model parameters. Using the GaLactic and Extragalactic All-sky Murchison Widefield Array survey eXtended (GLEAM-X), a low frequency radio survey conducted with the Murchison Widefield Array (MWA), we find that we are successfully able to recover an angular correlation function that is consistent with the Lambda-CDM cosmological model. We perform covariance analysis to get an estimation of the properties of the errors, and using these errors are able to fit a bias to the discrete tracers of the underlying matter distribution. Our results are consistent with previous studies on the topic, and provide further independent confirmation of the Lambda-CDMcosmological model.
[P019] “Towards an Epoch of Reionization Detection — Challenges in a pre SKA Era” – Aman Chokshi
As the host of the MWA and the future SKA-Low telescopes, Australia plays a key role in the efforts towards a first detection of the Epoch of Reionization signal. In this talk I present a overview of the latest innovations towards this goal from the Australian community – from end-to-end simulations to validate our processing pipelines to ranges of stringent quality metrics applied to our observed data to detect and discard data contaminated by active ionospheric conditions, radio frequency interference and instrumental malfunctions. I also touch on progress made towards understanding the all-sky sensitivity of our telescope which spans developing instrumentation to use satellites to measured varied beam models to propagating deformed beam models into cutting-edge calibration frameworks which could potentially improve EoR upper limits by a factors between 100-1000, and also exploring how a setting galactic plane of the horizon could impact the prospects of an EoR detection. Analysis techniques and instrumentation developed here will directly enable next generation science in the near SKA-Low era.
[P071] “First result from the CRAFT COherent upgrade (CRACO): Exploring transient radio sky on millisecond to second timescales” – Ziteng Wang
Short-duration radio transients are often associated with energetic events in the Universe. The discovery of more such transients will help us understand the critical information for these events, such as the progenitors and the key physical parameters of the event. In this talk, I will present the first results made using a new backend on the Australian Square Kilometre Array Pathfinder, CRAFT Coherent upgrade (CRACO), which enables us to record the correlated visibilities with tens of millisecond time resolution. This upgrade is helping us probe an hitherto unexplored part of the transient parameter space with a large field-of-view survey imaging telescope like ASKAP. We have so far discovered 15 new fast radio bursts (FRBs), 8 new pulsars/rotating radio transients, and 2 new ultra-long period transients (with a period of 44 mins and 6.5 hours respectively) in the first 2000 hours of our pilot survey. Out of these, notably, we’ve found that one source is a repeating FRB, one is a highly scattered FRB, and one is a slow-rotating pulsar (40 s). The discovery of these sources hints at the existence of a larger population of sources that was not previously known to exist. I will also discuss the future plan for CRACO including real-time detection and higher time-resolution data searching.
[P098] “ASKAP J1839-0756 – a ULPO candidate with a period of 6.45 hours” – Yu Wing Joshua Lee
Ultra-long period objects (ULPOs) represent a unique class of radio transient objects, with only a few having been identified to date. These objects emit highly polarised, coherent pulses with widths of tens of seconds to several minutes and periods ranging from a few tens of minutes to approximately an hour. Their location in the radio transient phase space clusters in an as-yet unexplored region near the boundary between coherent and incoherent sources, offering a possible connection between the emission mechanisms of both types. We present here the discovery of ASKAP J1839-0756 which emits ~90% linearly polarised radio pulses lasting ~1400 seconds every 6.45 hours. This makes it a ULPO candidate with the longest period recorded to date. The radio emission properties suggest a compact object origin, which can be a neutron star or a white dwarf that is either isolated or in a binary system. The spiky, short timescale sub-structure in the pulse is reminiscent of magnetars, while the steep spectral index of -2.7 is similar to the mysterious Galactic Centre Radio Transient. In this presentation, I will introduce recent observational results and possible progenitor models of this source, and discuss its position in the emerging ULPO population.
[P011] “Unveiling Long-Term Optical Variability Patterns in a Complete Sample of Broad Emission Line AGN” – Neelesh Amrutha
AGN with broad emission lines (Seyfert-1 galaxies) form a sequence of intermediate types based on the flux ratio between their broad Hβ line and narrow λ5007 [OIII] line. The sequence may be caused by nuclear dust obscuration as suggested by the traditional unification scheme, or by current accretion rates that deviate from the long-term averages as seen in the narrow lines. To date, fewer than 10 Seyfert AGN have been monitored over periods exceeding a decade. While the Six-degree Field Galaxy Survey (6dFGS: 2001-2009) provides optical spectra for ~600 Seyfert-1 AGN at z<0.1 in the Southern sky, we have obtained a second epoch of spectra over the past five years. We show that, on average, AGN with weak broad lines in the past show stronger lines now, while those with strong lines in the past show weaker lines now. This suggests that the narrow lines represent a long-term activity level, while the broad lines vary over timescales of decades in a range-bound manner and return from excursions to extremes. In this talk, we will highlight the key findings of our spectral comparison and discuss the use of eROSITA X-ray column densities to untangle the contributions of accretion and obscuration factors in the observed AGN variability.
[P036] “The evolution and drivers of gas turbulence in intermediate-redshift galaxies” – Yifan Mai
We measure the ionized gas velocity dispersion of star-forming galaxies in the MAGPI survey (z~0.3) and compare them with galaxies in the SAMI (z~0.05) and KROSS (z~1) surveys to investigate how the ionised gas dispersion evolves. We use a consistent method that forward models galaxy kinematics accounting for spatial substructure in emission line flux and beam smearing. We investigate the correlation between gas velocity dispersion and galaxy properties to understand the mechanisms that drive gas turbulence. We find that in both MAGPI and SAMI galaxies, the gas velocity dispersion more strongly correlates with the star-formation rate surface density (SFRD) than with other physical properties including mass, size, and SFR, and the average gas velocity dispersion is similar at the same SFRD bin for SAMI, MAGPI and KROSS galaxies. The results indicate that the mechanism relates to SFRD is the dominant driver of gas turbulence from z~1 to z~0, which may be stellar feedback and/or gravitational instability. The gas velocity dispersion of MAGPI galaxies is also correlated with the non-rotational motion of the gas, illustrating that in addition to star-formation feedback, gas transportation and accretion may also contribute to the gas velocity dispersion for galaxies at z~0.3. KROSS galaxies only have a moderate correlation between gas velocity dispersion and SFRD, and a higher scatter of gas velocity dispersion at the SFRD bin, in agreement with the suggestion that other mechanisms, such as gas transportation and accretion, are relatively more important at higher redshift galaxies
[P032] “Measuring the effective number of neutrino species with early Universe sound waves” – Abbe Whitford
Upcoming galaxy surveys aim to constrain the properties of neutrinos by constraining the effects of free-streaming particles in the early Universe, via a parameter known as the effective number of neutrino species. This is possible, because the presence of fast-moving free-streaming particles during the epoch in which sound waves were able to propagate through the primordial plasma, known as the Baryon Acoustic Oscillations (BAOs), induced a phase-shift in the sound waves. The over and under-densities formed by the sound waves at the moment they ceased to propagate seeded the Large Scale Structure that can be seen today as a peak in the correlation function of galaxies. It has been shown in the literature that it is possible to constrain the effective number of neutrino species by a parameterisation of the phase-shift that is induced in the BAO signal. In this work, we aim to measure this phase-shift in the BAOs measured by the DESI collaboration, which are the most precisely measured BAO signals to date. This provides an improved and less model-independent constraint on neutrinos, and any other particles that contribute to the effective species in the early Universe from cosmological data.
[P125] “The SAMI Galaxy Survey: On the importance of applying multiple selection criteria for finding Milky Way Analogues across environments” – Sujeeporn Tuntipong
Milky Way Analogues (MWAs) provide an alternative insight into the various pathways that lead to the formation of disk galaxies with similar properties to the Milky Way. In this study, we explore different selection techniques for identifying MWAs in the SAMI Galaxy Survey. We utilise a nearest neighbours method to define MWAs using four selection parameters including stellar mass, star formation rate (SFR), bulge-to-total ratio (B/T) and disk effective radius. Based on 15 different selection combinations, we find that including stellar mass and SFR is essential for minimising biases in the average MWA properties as compared to the Milky Way. Furthermore, given the Milky Way’s smaller-than-average size, selection combinations without disk effective radius result in MWAs being too large. Lastly, we find that B/T is the least important parameter out of the four tested parameters. Using all four selection criteria, we then define the top 10 most Milky Way-like galaxies in both the GAMA and Cluster regions. These most Milky-Way-like galaxies are typically barred spirals, with cold rotating disks, and reside in a wide range of environments. Surprisingly, we find no significant differences between the MWAs selected from the GAMA and Cluster regions. Our work highlights the importance of using multiple selection criteria for finding MWAs but also demonstrates potential biases in previous MWA studies.
[P066] “Direct interferometric image reconstruction with closure invariants and machine learning” – Samuel Lai
Image reconstruction from very-long baseline interferometric (VLBI) observations involving sparse sampling of the Fourier domain is an ill-posed deconvolution problem. Estimates of the source intensity distribution require robust algorithms and techniques to overcome the limitations caused by the incomplete sampling of the uv-plane. Notably, the final image can be sensitive to the interferometric calibration of station-based errors, which is particularly challenging at high frequencies. These details have substantial impact on some of the most significant VLBI discoveries in the past several years, including the results by the Event Horizon Telescope (EHT) collaboration. Alternatively, there are methods of direct interferometric imaging leveraging closure quantities, which are immune to such calibration errors. Recent research explored how simple machine learning models can use invariant closure quantities obtained from sparse aperture coverage to distinguish between various morphological classifications with >80% accuracy, improving with greater coverage. In this talk, we present a logical extension of this approach, by utilising deep learning and closure invariants to perform direct image reconstruction. We compare our image reconstruction with state-of-the-art VLBI imaging algorithms and show how our closure-only imaging yields comparable results, independent of gain and phase errors. This approach, which can be further extended for polarimetric imaging, offers an additional constraint on source morphology, ultimately improving the accuracy and reliability of sparse VLBI imaging results.
[P051] “Characterisation of Hidden Companions to Wobbling Stars” – Alex Wallace
Since its first data release, the Gaia mission has provided a wealth of knowledge about the precise positions and motions of nearby stars. From this, we can measure parallax and proper motion to high degrees of accuracy. However, if a star is orbited by an unseen companion, the companion’s gravitational pull causes the position measured by Gaia to be slightly distorted. This causes a discrepancy between the measured position and the expected position of a single star which is quantified by the reduced unit weight error (RUWE). A star’s RUWE value has previously been identified as a possible indicator of an unseen companion. In this talk, I present our method of identifying and characterising stellar and substellar companions based on astrometric measurements and the RUWE from Gaia. I show how we can constrain the mass of a companion as well as its orbital characteristics such as period and inclination. I show how this can be applied to the known binary systems as well as nearby planetary systems when combined with other methods and show how epoch data from Gaia’s next data release will vastly improve these results.
[P102] “A decade of Pulsars and Fast Transients with the Murchison Widefield Array” – Bradley Meyers
Pulsar and fast transient science with the Murchison Widefield Array (MWA) has been through a long and exciting journey, from the first high-quality detections of Crab giant pulses at low frequencies using an early prototype system, to the recent successful launch of an ambitious, all-southern-sky pulsar survey. The highly non-traditional path for high-time-resolution science has been dictated by enormous data rates and bespoke processing development tasks inherent to the facilitation and extraction of science. In this review, I will present a summary of some of the key milestones, highlighting examples of new science they have enabled and the people involved in making each step a possibility. I will also comment on the enormous science potential that can now be realised through ongoing large projects such as the SMART pulsar survey, and provide insights into the yet-untapped potential of the MWA to become a powerful low-frequency monitoring machine for pulsars and fast transients. Finally, now that SKA-Low construction is underway, leveraging the expertise built up by the MWA team regarding pulsars and fast-transient science will be invaluable for commissioning and verification activities in the near future.
[P017] “Exploring Millimetre Transients: Opportunities and Insights from Modern CMB Surveys and the Simons Observatory” – Justin Patrick Clancy
The millimetre transient sky is being explored in ever-increasing detail with modern CMB surveys, which now host sufficient resolution, sensitivity, sky coverage and cadence.
Synchrotron emission, probed extensively by CMB bands, is strongly associated with a range of transient events, such as gamma-ray burst reverse shocks, flaring stars, fast radio bursts, etc.
Studying synchrotron transient events in the millimetre offers a new avenue for constraining statistical properties, uncovering missing mechanisms, or even finding new microwave transients.
In this talk, I will provide an overview on the current state of millimetre transient astronomy and discuss new opportunities for studying synchrotron transient events.
I will also introduce the Simons Observatory CMB experiment and the transient detection pipelines currently under construction which will enable real-time millimetre transient discoveries in the near future.
[P129] “The curious case of twin fast radio bursts” – Apurba Bera
Fast radio bursts (FRBs) are brilliant short-duration flashes of radio emission originating at cosmological distances. Vast diversity in the properties of currently known FRBs, complex spectro-temporal structures and the fleeting nature of these events make it difficult to understand their progenitors and emission mechanism. The Commensal Real-time ASKAP Fast Transients (CRAFT) survey, with the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope, enables high time resolution spectro-polarimetric study of FRBs that helps us probe the physics of the emission source and its surrounding medium. In the curretly available CRAFT FRB sample we identified two apparently unrelated FRBs that show remarkable reseblance in pulse shape, rest-frame emission time-scales and polarization properties — which indicates that these two events are likely to have very similar progenitors. The observed properties of these two FRBs may be explained by emission from fast rotating neutron stars with spin periods comparable to the fastest known millisecond pulsar.
[P119] “The discovery and follow-up of four candidate binary millisecond pulsars via image-plane searches” – Flora Petrou
Binary millisecond pulsars (BMSPs) are important objects in testing fundamental physics. A population of millisecond pulsars (MSPs) may be responsible for the excess γ-ray emission observed in the Galactic center. Traditionally, these systems have been detected using pulsation searches, but this approach faces difficulties in the Galactic center due to the effects of scattering and dispersion. These difficulties are not an issue in the image plane, making it a more effective approach in detecting BMSPs in this region. The development of the Square Kilometer Array (SKA) precursors allows for image-plane searches that are more sensitive to detecting such systems and allows us to search a wide frequency range that was not previously available.
A recent monitoring campaign of the Murchison Widefield Array has led to the discovery of four new transients. Their eclipse-like variability, steep spectra, and γ-ray associations imply that they could be BMSPs producing both radio and γ-ray emission. In this talk, I will present the discovery and follow-up of these four sources. We have observed them with ASKAP Variables and Slow Transient survey (VAST), Parkes radio telescope ‘Murriyang’, upgraded Giant Metrewave Radio Telescope, and the Australia Telescope Compact Array. I will also discuss the possible reasons behind the non-detection of the pulses, constraints on the companion stars, theories regarding the eclipse mechanism, and properties of the eclipsing medium. Finally, I will outline our plans to search for more of these sources with VAST, providing further opportunities for discovery and study.
[P065] “Discovery of the first millisecond pulsar in the Galactic Centre” – Marcus Lower
The quest to find pulsars in and around the Galactic Centre has been arduous and largely unsuccessful, with only a handful of long-period pulsars having been found in blind searches. This is in spite of population synthesis studies and the Fermi GeV excess indicating that a substantial pulsar population should exist within the centre of our Galaxy. Using Murriyang, the 64 m Parkes radio telescope, we conducted a search for pulsars centred on a previously identified compact radio source embedded in a non-thermal radio filament known as the “Snake”. We discovered a new millisecond pulsar, PSR J1744-2946, bound in a 4.8 hr orbit around a > 0.05 Solar mass companion. The high dispersion measure of 673 pc/cc is the largest of any millisecond pulsar found to date and cements it as the first object of its kind to be found in the Galactic Centre. In this talk I will describe the properties of this remarkable pulsar, what this discovery means for upcoming high-frequency surveys of the Galactic Centre and how its potential association with a non-thermal radio filament may have resolved the mystery of how these large scale magnetic structures are illuminated.
[P020] “Late-Time Supernovae Radio Re-brightening in the VAST Pilot Survey” – Kovi Rose
I present our pilot study for the detection of core-collapse supernovae radio re-brightening at very late times. Radio emission from supernovae can reveal information about the progenitor star’s mass-loss history as well as properties of the supernovae, like the shockwave velocity and magnetic field strength. Supernova lightcurves tend to rise and fall on timescales of weeks to months and the radio emission is understood to be produced as the shockwave propagates through the circumstellar material. Targeted observations of supernovae have resulted in the detections of re-brightening events several years after the optical discovery. We used observations from the Rapid ASKAP Continuum Survey to identify 8 potential candidates of late-time supernova re-brightening. We modelled the radio evolution of these supernovae based on detections from ASKAP surveys, follow-up observations, and measurements in the literature. I will demonstrate how this approach can be used to find >100 supernovae re-brightening events with ASKAP in the coming years.
[P033] “Things That Go Bump In The Night: Transits and Transients With The Harlingten 50cm Telescope” – Thomas Plunkett
We are arriving at an exciting moment for time-domain astronomy: the beginning of next-generation surveys and telescopes, such as LSST (Ivezić et al. 2019) and RST (Akeson et al. 2019). With the new facilities becoming operational in the next decade, we must prepare ourselves for the surge of data and discoveries to come. One component of this will be in detailed modelling/simulation of expected capabilities of these telescopes. Another crucial aspect is the use of current ground-based facilities to discover and follow-up on potential targets for these future missions. The importance of this is two-fold. It will allow for the optimisation of scheduling and time-allocation through prioritisation of important targets or fields. It also provides the community with insights into the data reduction and modelling techniques that will be required to maximise the scientific outputs from the collected data.
The University of Tasmania Greenhill Observatory (UTGO) is one such facility which aims to contribute to follow-up efforts, specifically in areas of exoplanetary transits and transient phenomena.With the addition of the new Harlingten 50cm telescope, we aim to increase our scientific output and educational opportunities. In this sparkler, we will give a brief outline of the work done in 2023 to validate the new telescope’s performance, along with characterising the observatory site. This includes investigating the weather trends and observing conditions, along with quantifying the image quality and limiting magnitudes for the telescope.
[P058] “A long-period radio transient in a binary orbit” – Natasha Hurley-Walker
Using the Murchison Widefield Array, we have discovered a new long-period radio transient, one of an emerging class of objects that produces highly polarised radio pulses that repeat on a slow cadence. Their progenitor is unknown: they could be neutron stars, white dwarfs, or something even more unexpected. Published examples repeat every ~20 minutes; our new discovery repeats on a surprisingly long period of 3 hours. We describe the observations of this source, including historical MWA observations that indicate a long history of activity, high time resolution data from MeerKAT, and a likely optical counterpart. The system appears to be a binary, and analysis of the timing residuals may for the first time constrain the mass of the radio emitter.
[P050] “The MAGPI Survey: Drivers of kinematic asymmetry in the stars and gas of z~0.3 galaxies” – Ryan Bagge
Stellar and gas kinematics are sensitive to the underlying mass distribution within galaxies, hence they are useful to understand a galaxy’s assembly and evolution. Similarly, gas kinematics can be sensitive to elements of galaxy evolution that stellar kinematics are not (e.g., gas flows, feedback, etc.). The dynamics of galaxies along the line-of-sight can be modeled as a point-symmetric function, but deviations from symmetry can be caused by mergers, interactions, and secular galaxy evolution processes. I will discuss how we use a sample of galaxies from the Middle Ages Galaxies Properties in Integral Field Spectroscopy (MAGPI), with kinemetry, to investigate what drives the kinematic asymmetry in both the stars and gas. We find a similar distribution of stellar kinematic asymmetries in galaxies where we detect ionised gas, and those we do not; suggesting that whatever drives the asymmetry does not always lead to gas removal, or that the gas was already removed before the stellar asymmetries increased. We also find that when old mean-stellar-ages (log (Age/yr)>9) have gas, they will display larger asymmetry in their gas, compared to their stars; whereas younger galaxies will display larger asymmetries in their stars. I will then offer some conclusions regarding our results, and how they highlight the wealth of information about galaxy evolution that is available when comparing the kinematics of stars and gas holistically.
[P003] “Partial tidal disruption events: The elixir of life” – Megha Sharma
In our Galactic Center, about 10,000 to 100,000 stars are estimated to have survived tidal disruption events, resulting in partially disrupted remnants. These events occur when a supermassive black hole (SMBH) tidally interacts with a star, but not enough to completely disrupt the star. We use the 1D stellar evolution code Kepler and the 3D smoothed particle hydrodynamics code Phantom to model the tidal disruption of 1 solar mass, 3 solar mass, and 10 solar mass stars at zero-age (ZAMS), middle-age (MAMS), and terminal-age main-sequence (TAMS). We map the disruption remnants into Kepler in order to understand their post-distribution evolution. We find distinct characteristics in the remnants, including increased radius, rapid core rotation, and differential rotation in the envelope. The remnants undergo composition mixing that affects their stellar evolution. Whereas the remnants formed by disruption of ZAMS models evolve similarly to unperturbed models of the same mass, for MAMS and TAMS stars, the remnants have higher luminosity and effective temperature. Potential observational signatures include peculiarities in nitrogen and carbon abundances, higher luminosity, rapid rotation, faster evolution, and unique tracks in the Hertzsprung-Russell diagram.
[P095] “Probing the magneto-ionic interstellar medium with pulsars using SKA-Low precursor stations” – Christopher Lee
The low-frequency Square Kilometre Array telescope (SKA-Low) will be a groundbreaking instrument for a variety of pulsar astrophysics, including advancing our understanding of pulsar emission physics and using pulsars as powerful probes of the magneto-ionic interstellar medium. The precursor SKA-Low stations are playing a crucial role in preparing for SKA-Low science; an initial census yielded detections of 22 known pulsars using the modest sensitivity of the early prototyping system. Motivated by these encouraging results, we have carried out high-cadence observations of the Vela pulsar – the brightest pulsar in the southern sky – utilising the large fractional bandwidth provided by the upgraded capability of the prototype stations. This yielded precision measurements of Faraday rotation and dispersion imparted on the pulsar signals by the interstellar medium. By combining our data (spanning over a year) with historical data from the published literature, we have modelled long-term variations in the Faraday rotation measure (RM) and dispersion measure (DM) over the past two decades. Our analysis has revealed significant changes in both the mean line-of-sight electron density and magnetic field strength toward the Vela pulsar, which implies compact magneto-ionic structure on physical scales of ~1-2 AU. This is the first observational evidence of interstellar magnetic field structure at such small scales. As well as providing an important validation of polarimetry, our work underscores the pulsar monitoring capabilities of SKA-Low stations, and the niche science opportunities they offer for high-precision polarimetry and probing the microstructure of the magneto-ionic interstellar medium.
[P093] “Decomposed Infrared Luminosity Functions of High-Redshift Galaxies and AGN using CIGALE” – Daniel Lyon
ZFOURGE, the FourStar Galaxy Evolution Survey, stands as a pivotal endeavour in probing the depths of high-redshift galaxy evolution through infrared observations. This study taps into these observations to investigate and extend the infrared luminosity functions and spectral properties of distant galaxies and active galactic nuclei (AGN) to z ~ 6. Using the SED decomposition software, CIGALE, I have generated bolometric infrared luminosity functions and star formation rate densities, which are crucial for probing the processes that drive galaxy formation. Our approach uses decomposed SEDs to effectively mitigate the effects of AGN, enabling more precise measurements. Additionally, we provide AGN luminosity functions that offer valuable insights into their evolutionary significance and impact on galaxy co-evolution. In this presentation, I will outline my approach and discuss the broader implications of my findings, emphasising how they contribute to our understanding of galaxy and AGN evolution across cosmic time.
[P080] “The origin of magnetic fields in galaxies” – Amit Seta
Magnetic fields are a dynamically important component of galaxies but are often overlooked due to the complexities involved in theory, numerical modelling, and interpretation of observational data. In the early universe, magnetic fields are known to be significantly weaker (~ 10^{10} times) than those observed in the Milky Way and local galaxies today. So, a natural question arises: what is the origin of these galactic magnetic fields? The answer lies in turbulent dynamos, the mechanism by which the turbulent kinetic energy in galaxies is converted to magnetic energy. This talk will review the origin and evolution of magnetic fields in galaxies from the early to the present-day universe, with a focus on comparing turbulent dynamo theory with radio polarisation observations and discussing future prospects with the Square Kilometre Array.
[P056] “Insights on high-redshift galaxy-AGN coevolution from comprehensive demographic analysis of z ~ 5 ultraluminous quasars” – Samuel Lai [R]
The inaugural year of science with the James Webb Space Telescope has been updating our understanding of galaxy and active galactic nuclei (AGN) co-evolution in the early Universe. New spectroscopically confirmed faint AGN with supermassive (106 – 109) black holes (SMBHs) are inferred to be an order of magnitude more abundant than expected from UV-selected AGN samples. Moreover, many such AGN are found to be over-massive relative to their host galaxy’s stellar population (offset from the local MBH – M* relation). These observations provide tantalising evidence that the formation of SMBHs in massive galaxy precursors precede the development of dominant stellar components. In this talk, we present a comprehensive demographic analysis using spectroscopic follow-up observations of a highly complete sample of z ~ 5 ultraluminous quasars identified using the SkyMapper Southern Survey. Our analysis indicates that the supermassive black holes which constitute the ultraluminous quasar population have slowed significantly in their mass growth by z ~ 5. However, their observed black hole masses require that they must have grown much more rapidly in the earlier Universe, aligning with the JWST findings of SMBH growth outpacing galactic components. The observations necessitate cosmological models of the early Universe to include the early formation of a substantial population of ultracompact galaxies hosting efficiently accreting AGN.
[P117] “Hydrodynamical jets in three flavors: insights for cosmological simulations” – Nikolaos Maragkakis
Active Galactic Nuclei (AGN) feedback is a critical ingredient in modern cosmological simulations but must be implemented in a subgrid fashion. Different simulation codes typically use different implementations of AGN feedback and as a result produce galaxies with distinct properties, which complicates detailed comparisons between different simulation results – it is unclear whether the treatment of hydrodynamics or the feedback implementations are to blame. To explore this, we present results from idealized hydrodynamical tests and AGN jets obtained using three different codes: Swift, Arepo and Pluto. We include tests that are relevant for feedback processes – the Sod Shock Tube and the Sedov Blast. The different simulation codes produce similar results that are consistent with known analytic solutions for a broad range of resolutions. We also carry out tests in which self-similar AGN jets expand into a uniform as well as a stratified medium. In general, there is good agreement between jets simulated using different codes at spatial resolutions relevant for cosmological simulations.
[P163] “GLEAM-X and young AGN: What’s available and what’s next” – Kat Ross
The GaLactic and Extragalactic All-sky MWA eXtended (GLEAM-X) survey boasts twice the resolution, and up to an order of magnitude higher sensitivity to its predecessor the GLEAM survey. In 2020, observations for GLEAM-X were completed and the first data release covering 2,000 square degrees down to an RMS noise level of <1.5 mJy/beam was recently released. The second data release, covering an RA range from ~20h to 6h and Dec<+30, has an improved RMS noise level of <1mJy/beam, and ~650,000 sources with spectral fitting and now complete. We will also present the classification of the largest catalogue to date of peaked spectrum sources (PSS), believed to be the early stages of typical radio loud active galactic nuclei, increasing the known number of PSS by an order of magnitude. In this talk, we will showcase early science results from the second data release including spectral variability of PSS, evolution and ageing of AGN, cosmology, and tomography of ionospheric disturbances and present an update on the progress of the final GLEAM-X data release.
[P014] “Cosmic Origins of AGN and Star Formation Unveiled by the James Webb Space Telescope” – Jordan D’Silva
TheJames Webb Space Telescope(JWST) is revolutionising our understanding ofstar formation and the growth of super massive black holes. However, the interface of these two processes, especially beyond z=5, is not well understood as their contributions to the spectral energy distributions (SED) of galaxies are almost equivalent and requires careful disentangling.Reconciling the coevolution of these two processes is critical if we are to further advance our understanding of how galaxies formed and evolved shortly after the Big Bang.
I will discuss our photometry of z>5 galaxies, carefully prepared by a custom data reduction pipeline and leverages the full strength of JWST imaging. We then analysed the light distributions using the SED fitting software ProSpect that simultaneously accounts for star formation and active galactic nuclei (AGN) when interpreting the SEDs of our JWST detected, distant galaxies.
We found that accounting for an AGN component is critical to explain the physics underpinning the SEDs of among the first galaxies to ever exist in the Universe. We found that accounting for AGN can reduce the final stellar masses by as much as 4 dex and the resultant cosmic star formation density by 0.4 dex at z>5.
Finally, I will discuss our complete catalogue of z>5 stellar masses, star formation rates and AGN luminosities that we are using to further unveil the mysteries of the high-redshift frontier.Our results have significant implications for the abundance of AGN at z>5, the progenitors of massive quasars and the sources of reionisation.
[P053] “Unveiling the diverse formation histories of disc galaxies with present day observables” – Katy Proctor
In the Lambda Cold Dark Matter cosmological model, mergers play a significant role in galaxy formation. The ubiquity of nearby disc galaxies suggests that stellar discs can emerge from a variety of merger histories: while some disc galaxies experience quiet merger histories, simulations suggest that stellar discs can also survive, or quickly reform after, significant merger events. Understanding whether these distinct formation pathways can be inferred from present day observables is an active area of research. We address this issue by studying the formation of disc galaxies in the EAGLE cosmological simulations. We apply a novel galaxy decomposition technique based on stellar dynamics to isolate the disc, bulge, and stellar halo components of a large sample of Milky Way mass galaxies. Our results reveal that the present day disc population arises from diverse pathways: while two thirds of our sample experience quiet merger histories, one third undergo at least one significant merger at z<1. We show that these mergers happen preferentially in the plane of the disc component. Coplanar mergers can contribute a significant amount of mass directly to the disc component without affecting the morphology of the central galaxy or contributing to the stellar halo. We also quantify the impact that these mergers have on the structure of stellar discs, discussing the feasibility of probing different formation pathways with present day observables.
[P021] “A new approach to beam-smearing: moving towards non-parametric models for all kinematic types” – Isaac Kanowski
Obtaining accurate measurements of galaxy kinematics is key to studying their internal properties and thereby better understanding the factors that drive galaxy formation and evolution. This is particularly true for observations at cosmic noon (z ~ 1-3) and higher redshift, which can constrain measurements of disk stability, gas abundance and turbulence in the early universe. However, IFS studies, particularly those at high redshift, are impacted by the observational effect of beam smearing, which artificially decreases the magnitude of measured rotational velocities and significantly increases velocity dispersions. Beam smearing substantially inhibits our ability to compare galaxy properties across cosmic time as it is difficult to accurately account for this effect across a large range of galaxies. Most current state-of-the-art methods used to account for beam smearing at high redshift have been optimised to fit relatively high S/N disk-like galaxies and have therefore been applied to a biased subsample of IFS datasets.
Aiming to overcome this, we have adapted the existing HI-line fitting code ROHSA with regularisation to create an adaptable new tool that derives deconvolved kinematic maps of galaxies at high redshift without assuming an intrinsic disk model or a particular line-transition. I will first summarise the forward modelling approach used by our code to account for beam smearing in a spatially non-parametric way. I will then present the results of applying our code to legacy KMOS data observed by the KMOS3D survey including galaxies of different kinematic types.
[P148] “The Galactic and Extragalactic All-sky MWA Survey at 300 MHz” – Stefan Duchesne
The Murchison Widefield Array (MWA) has over the last ten years conducted multiple surveys – most notably the Galactic and Extragalactic All-sky MWA survey (GLEAM). GLEAM was observed at five frequencies initially, covering 72 to 231 MHz, but was also followed up by similar observations at 300 MHz. While 300 MHz MWA data have been a much more difficult calibration and imaging challenge, due to recent work by Cook et al. (2021) we have been able to begin processing the 300 MHz data and produce images over the sky visible to MWA. This sparkler/poster will cover the progress of the GLEAM 300 MHz survey (tentatively GLEAM-300), showcasing the images and the catalogue being produced as part of this survey.
[P030] “The Rubin Observatory in Simulated Universes: Characterizing tidal features around galaxies in cosmological simulations” – Aman Khalid
Low surface brightness tidal features around galaxies serve as indicators of recent mergers, offering invaluable insights into the role of mergers in galaxy evolution. Rubin Observatory’s Legacy Survey of Space and Time (LSST) will provide an unprecedented sample of tidal features around millions of galaxies. These observations will provide snapshots of galaxies at a particular stage of their evolution. To decipher their contributions to galaxy evolution we must examine them with reference to cosmological hydrodynamical simulations. We study tidal features around low-redshift galaxies in LSST-like mock images from the NewHorizon, EAGLE, IllustrisTNG and Magneticum cosmological hydrodynamical simulations. We characterise the simulations in a manner directly comparable to LSST observations. I will reveal how tidal feature frequencies vary as a function of stellar and halo mass across the simulations. Moreover, I will highlight the similarities and differences and discuss the roles of simulation resolution, calibration and sub-grid physics models in the occurrence of visually detectable tidal features. The predictions discussed here can be verified directly with LSST observations.
[P039] “New Results on the Giant Pulse Detections from J1823-3021A Observed with the MeerKAT UHF Baseband High Time-resolution Data” – Chien-Chang Ho
Giant Pulses (GPs) are remarkably intense bursts of radio emission from pulsars that can exceed the typical single pulse strength by many orders of magnitude. They are most typically seen in young MSPs and Crab-like pulsars. Abbate et al. 2020 studied the milli-second pulsar (MSP) J1823-3021A which is the most active GP emitter in the globular cluster (GC) NGC6624 with MeerKAT L-band (856-1711 MHz). Here we present our observations of the same target, taken in the UHF band (580-1015 MHz) with two times better time resolution (5.3 μs/bin). Due to this advantageous setup, and the steep spectral index of the pulsar, we detected a significantly higher number of GPs from this MSP than in all previous studies. GPs from this pulsar mainly come at 2 different phases within a single rotation of the pulsar. They have a well fitting power-law to their energy distribution, are typically broadband and have steep spectral indices. We have measured polarization of the pulsar and the GPs. Overall, they are not significantly polarized. The high time resolution of the data allows us to explore the temporal structure of the GPs with unprecedented resolution which makes this the largest sample of GPs with high time resolution. Taking advantage of this, we have measured the scattering of the GPs for the first time for this pulsar. We also briefly discuss the connection between GPs and the repeating FRBs from a GC in M81.
[P107] “Deep Field Imaging of the GAMA9 and GAMA23 Regions” – Sean Paterson
Thousands of observations of the well-studied Galaxy and Mass Assembly (GAMA) fields, GAMA9 and GAMA23, have been conducted with the MWA (Murchinson Widefield Array) radio telescope for the MWA Interestingly Deep Astrophysical Survey (MIDAS) and the GAMA23 OverwheLming Deep (GOLD) survey. Here we present deep images of the GAMA9 and GAMA23 fields centered at a frequency of 215.68\,MHz with a bandwidth of 30.72\,MHz, produced from these observations obtaining an RMS below 1\,mJy/beam. These deep field images will assist in determining source counts to produce low-frequency radio luminosity functions that can be used to analyse radio galaxy evolution. In addition, we provide a detailed description of the automated Deep Imaging Pipeline (DIP) that enabled the creation of these images. DIP was adapted from the pipeline used in the GaLactic and Extragalactic All-sky MWA X (GLEAM-X) survey with improvements in the cleaning for deep imaging and automation to allow large batch processing with minimal user input.
[P145] “ARC Centre for Excellence for Optical Microcombs for Breakthrough Science (COMBS)” – Michael Murphy
COMBS is a new, multi-disciplinary ARC Centre for Excellence devoted to taking the new technology of optical microcombs out of the laboratory and into fields where they can enable new scientific breakthroughs. One such area is astronomy, where optical frequency combs are already used to calibrate the wavelength scale of high-resolution spectrographs – so-called “astrocombs”. However, these systems are large and heavy (like a fridge) and less than reliable, particularly at visible wavelengths. Microcombs are, in essence, miniaturised comb systems that have the potential to reduce the size, complexity and cost of astrocombs, and greatly increase their reliability. This would enable high-precision spectroscopic experiments requiring accurate wavelength measurements over long time-scales, possibly even decades, on both large and small telescopes alike.
I will introduce COMBS, briefly highlight some aspects other astronomers may be interested in, and show how you can get involved.
[P092] “Supernovae and lookalike transients at early times” – Anais Moller
Early supernovae observations can provide us with insights on their progenitors and explosion mechanisms. However, at early stages supernovae and other transients can resemble and thus their selection for follow-up is challenging. In this talk, I will present methods to identify early supernovae in large surveys and explore the diversity of SNe Ia and their lookalikes.
I will present results for two machine learning algorithms applied to identify early SNe Ia in DES and ZTF. I will describe the main transients that resemble SNe Ia in these surveys and explore limitations on these classifications. I will then show a new method to improving these early classifications with an Active Learning recommendation system.I will conclude with a projection of the impact of this system in the era of the Vera C. Rubin Observatory LSST.
[P149] “Testing fundamental physics with stellar twins” – Michael Murphy
The Standard Model of nature’s laws provides no explanation for the fundamental constants, like electromagnetism’s strength, α. It is therefore up to experiments to test whether fundamental constants are, indeed, constant and universal, or instead vary and depend on other physical parameters. I will describe a new probe of α’s constancy within our Galaxy – stellar twins – and show our first results from solar twins which constitute the best astronomical measurement of α so far. Archival spectra of red clump stars also demonstrate that these much more luminous stars can probe α with the same technique, meaning we can compare the spectra of red clump stars near the Galactic Centre with local ones to measureα. Indeed, our goal is to map α across the Milky Way and, importantly, its widely-varying dark matter density field. This will be a completely new, direct test of physics beyond the Standard Model.
[P070] “EMU/GAMA: A Technique for Detecting Active Galactic Nuclei in Low Mass Systems” – Jahang Prathap P K
We propose a new method for identifying active galactic nuclei (AGN) in low mass (M* >= 1010MSun) galaxies. This method relies on spectral energy distribution (SED) fitting to identify galaxies whose radio flux density has an excess over that expected from star formation alone. Combining data in the Galaxy and Mass Assembly (GAMA) G23 region from GAMA, Evolutionary Map of the Universe (EMU) early science observations, and Wide-field Infrared Survey Explorer (WISE), we compare this technique with a selection of different AGN diagnostics to explore the similarities and differences in AGN classification. We find that diagnostics based on optical and near-infrared criteria (the standard BPT diagram, the WISE colour criterion, and the mass-excitation, or MEx diagram) tend to favour detection of AGN in high mass, high luminosity systems, while the “ProSpect” SED fitting tool can identify AGN efficiently in low mass systems. We investigate an explanation for this result in the context of proportionally lower mass black holes in lower mass galaxies compared to higher mass galaxies and differing proportions of emission from AGN and star formation dominating the light at optical and infrared wavelengths as a function of galaxy stellar mass. We conclude that SED-derived AGN classification is an efficient approach to identify low mass hosts with low radio luminosity AGN.
[P159] “In a world of increasing automation and AI, what is the role of the future astronomer?” – Vanessa Moss
The onset of automation and artificial intelligence across all industries and fields is rapidly increasing, and astronomy is far from immune. Machine learning has already been widely applied in analysis of astronomy data sets, and we are seeing the same trends within the observatory context through the direct application of these technologies to improve efficiency and productivity of telescope operations. But in the case where technology can replace or augment previous human effort across a wide range of activities in astronomy, a key question to ask is: what is the role of the human astronomer in the coming decade, and where is their expertise best applied?
I will present a brief overview of current work in this space in the context of ASKAP, with direct reference to our active project within the CSIRO Collaborative Intelligence (CINTEL) Future Science Platform. Our findings so far suggest that the balance between AI and human effort is unlikely to be a fixed ratio but instead something that evolves over time with increased trust in AI and automated approaches, and that the role of the human expert will generally gravitate towards the exploratory, poorly defined and creative areas of problem solving.
[P190] “Deriving Stellar Parameters and abundances: Employing “The Cannon” to Bridge GALAH-DR4 to GAIA-RVS Spectra” – Pradosh Barun Das
The enormous spectroscopic datasets from current astronomical surveys provide an unprecedented opportunity to explore the stellar populations of the Milky Way and its surroundings. The largest surveys range from several million stars (e.g., LAMOST) to the roughly quarter-billion stars observed with Gaia XP spectra. These survey data are generally at low or moderate spectroscopic resolutions, yet the “gold standard” for determining stellar parameters and elemental abundances remains high-resolution spectroscopic data. We have usedThe Cannon, a largely Australian-developed, data-driven method to transfer labels from high-resolution reference data to lower-resolution data, specifically applying stellar parameters and abundances derived from GALAH data (GALAH iDR4) to Gaia RVS spectra (Gaia DR3). We trained our data model on ~14000 selected targets common to both the surveys, utilising the stellar labels from GALAH. With this model, we are able to consistently predict stellar parameters such as Teff, log g, [Fe/H], and abundances of several alpha elements for over 800,000 Gaia RVS spectra. Using stars from several open and globular clusters present in the Gaia RVS catalogue, we have validated our metallicity estimates. Finally, for a subset of this sample with predicted log g < 3.5 (i.e., giants) we are able to measure the abundances of several neutron-capture elements, illustrating the exciting potential of this method for reliably determining stellar parameters and abundances from medium-resolution Gaia RVS spectra – a dataset which, by the end of the Gaia mission, is expected to include over 30 million stars.
[P047] “Precise Pinpointing of Fast Radio Bursts using the Australian Square Kilometre Array Pathfinder” – Akhil Jaini
Fast Radio Bursts (FRBs) are enigmatic cosmic phenomena characterized by millisecond-duration bursts of intense radio emission. Accurate localisation of FRBs is essential not only for unraveling their environments but also for leveraging them as powerful astrophysical and cosmological probes. While localisation with a precision of several arcseconds is sufficient to associate FRBs with their host galaxies at intermediate redshifts (z<0.5), at higher redshifts (z>1) sub-arcsecond localisation precision is highly desirable. The Australian Square Kilometre Array Pathfinder (ASKAP) is a 36-element interferometer that has emerged as a leading facility for FRB discovery and localisation.
In this study, we present a comprehensive methodology aimed at correcting systematic astrometric offsets within the Rapid ASKAP Continuum Survey (RACS) catalogue, which is used to precisely pinpoint FRBs discovered by ASKAP. Any astrometric errors in RACS, arising from instrumental and observational effects, impact the precise determination of FRB positions. Our approach involves crossmatching RACS sources with the Wide-field Infrared Survey Explorer (WISE) catalogue. By modeling and correcting the astrometric discrepancies, the median offsets in RA and DEC were reduced from 0.58 and -0.26 arcseconds to 0.00, with a 1-sigma confidence interval of ±0.20, in both cases. The resulting refined astrometry enables more precise pinpointing of FRB locations, contributing to the scientific yield from ASKAP data products.
This work establishes a critical foundation for future investigations. Leveraging the corrected RACS catalogue, we anticipate sub-arcsecond precision localisations for all FRBs detected by ASKAP.
[P144] “Photometric Activity Cycles in fast-rotating Stars: Revisiting the Stellar Activity Cycle Branches” – Deepak Chahal
Our study aims to detect photometric activity cycles (~11-year solar cycle) of stars across different evolutionary stages, providing valuable constraints into the generation of magnetic activity cycles via stellar dynamo mechanisms and their dependence on fundamental stellar parameters. We analyzed activity cycles in 189 fast-rotating G-K-type main-sequence and evolved stars. Employing a novel methodology, we combined data from state-of-the-art photometric time-series surveys (ZTF–ASAS-SN–Kepler) to construct a 14-year time-series, facilitating longer cycles similar to 11-year solar cycle. Additionally, we investigated whether the brightness variations are linked to specific features on the stars’ surfaces, like bright faculae or dark starspots. Our findings reveal that fast-rotating G-K-dwarfs display longer activity cycle periods (Pcyc>4-5 years), similar to slow-rotating stars (Prot>20-25 days), suggesting no clear link between cycle length and rotation periods. It has been established that there exist two distinct branches in the cycle–rotation diagram—active and inactive—indicating two types of dynamo behavior. However, our sample did not exhibit a clear trend aligned with the active branch, with many stars falling in the intermediate region between the active and inactive branches. Our results underscore that the dichotomy between active and inactive branches may not be as definitive for main-sequence stars, particularly the active branch. Moreover, our Sun, positioned in the intermediate region, may not be anomalous in this respect. Overall, our findings suggest that the processes driving activity cycles in fast-rotating stars may be more intricate than previously assumed, suggesting the presence of deeper dynamo mechanisms rather than near-surface ones.
[P166] “New robust merger rates at intermediate redshifts using the Deep Extragalactic VIsible Legacy Survey (DEVILS)” – Melissa Fuentealba Fuentes
Mergers are the collision of two or more galaxies, resulting in a larger, more massive system. These events are fundamental to our understanding of the processes that drive both the evolution of the structure/morphology of galaxies and the redistribution of stellar mass in the Universe. Therefore, determining the fraction and properties of mergers across cosmic time is critical to understanding the formation of the Universe we see today. There are multiple techniques for identifying mergers at different stages of their interaction, each providing its insights and complications. One such technique selects pre-merger galaxies through the identification of galaxy pairs that are close in both radial position and velocity. While robust, this methodology requires spectroscopic samples to be highly complete and has so far been limited to the relatively local Universe (z<0.2, i.e. from GAMA). This is set to change with the next generation of galaxy redshift surveys (e.g. WAVES-deep), where we will obtain comparable spectroscopic samples of galaxies extending to much earlier times. In this talk, I will present the identification of galaxy pairs at 0.2
Cosmic reionization, a pivotal epoch in the history of the Universe, marks the last phase transition when the Universe became fully ionized. A commonly held belief is that the Lyman-continuum (LyC) photons are the primary contributors of reionization. But the direct detection of LyC photons at z > 4 is almost impossible due to increasing neutral fraction of the intergalactic medium (IGM). Lyman-α (Lyα) emission line of the Hydrogen atom serves as an alternative and an indirect probe of the LyC photon escape and hence the Epoch of Reionization (EoR). Complex radiative transfer of Lyα photons leads to a variety of emerging Lyα spectra. We recently reported the discovery of three double-peaked Lyα emitters (LAEs) exhibiting strong blue-peak emission at 2.9 ≲ z ≲ 4.8 in the VLT/MUSE data. The one at z = 4.8 is a compact system and stands as the highest-redshift strong blue-peak LAE ever detected. A stronger blue peak captures an early evolutionary phase of the galaxy when cold accretion flows dominate. These strong blue-peak systems suggest inflows of gas along the line of sight and a low column density of neutral Hydrogen (HI) through which LyC photons can escape. The observed overall trend of decreasing peak separation with increasing radius is supposed to be controlled by HI column density and gas covering fraction. These findings shed light on the complex interplay between Lyα emission, gas kinematics, and ionizing radiation properties, offering valuable insights into the evolution and nature of high-redshift galaxies and how they contribute to reionization.
[P090] “The Cherenkov Telescope Array Observatory for Gamma-Ray Astronomy: Current Status, Linkages to Australian Astronomy, and Next Steps.” – Gavin Rowell
The Cherenkov Telescope Array Observatory (CTAO – www.ctao.org [//www.ctao.org]) will provide a paradigm shift in gamma-ray astronomy. It will deliver gamma-ray images reaching sub-arcminute resolution and provide orders of magnitude improvement in the search for gamma-ray transients. CTAO is fully funded to realise it’s ‘alpha’ array of telescopes at it northern and southern sites. Construction at both sites is well underway with early science from the first northern telescope already available.
This presentation will summarise the current status of the CTAO and its linkages to Australian radio and optical astronomy activities. Seven Australian institutions are currently involved in CTAO, contributing FTE effort towards observations planning and analysis techniques, funding for telescope hardware, and hardware directly from Australian industry. We will also look ahead towards CTAO’s full operations which will overlap the SKAO era.
[P005] “The Widefield Spectroscopic Telescope – surveying the Universe near and far” – Matthew Colless
The Widefield Spectroscopic Telescope (WST) is a proposed 12-metre survey facility with simultaneous operation of a large field-of-view (3 sq.deg.), high-multiplex (20,000) multi-object spectrograph (MOS) and a giant 3×3 arcmin integral field spectrograph (IFS). In scientific capability, these specifications place WST far ahead of existing and planned facilities. In only 5 years of operation, the MOS would target 250 million galaxies and 25 million stars at low spectral resolution plus 2 million stars at high resolution. Without needing pre-imaged targets, the IFS would deliver 4 billion spectra offering many serendipitous discoveries. WST will fill a crucial gap in astronomical capability and work in synergy with future ground and space-based facilities. It will address outstanding scientific questions in the areas of cosmology; in galaxy assembly, evolution, and enrichment, including our own Milky Way; in the origin of stars and planets; and in time domain and multi-messenger astrophysics. WST’s uniquely rich dataset may yield unforeseen discoveries in many of these areas. The telescope and instruments will be designed as an integrated system and will mostly use existing technology, with the aim to minimise the carbon footprint and environmental impact. We will propose WST as the next ESO project after completion of the 39-metre ELT. The WST consortium includes Australian institutions, together with ESO and institutions in 9 European countries.
[P161] “The BIGCAT upgrade for the Australia Telescope Compact Array” – Elizabeth Mahony
The Australia Telescope Compact Array has been a cornerstone of Australian radio astronomy for over 30 years. The BIGCAT upgrade, short for the Broadband Integrated GPU Correlator for ATCA, is currently underway and represents a complete overhaul of the entire backend of the ATCA, replacing every aspect of the telescope chain except the antennas and receivers (what we term the “front-end” of the telescope). This upgrade will double the instantaneous bandwidth from 4 to 8 GHz and provide a lot more flexibility in spectral line resolution. In this talk I will present an overview of the BIGCAT upgrade and detail the science commissioning plans for when BIGCAT is installed in the second half of this year.
[P069] “The future of radio astronomy with ASKAP.” – Aidan Hotan [R]
CSIRO’s ASKAP radio telescope in Western Australia is now conducting a wide range of Survey Science Projects designed to run for 5 years. Science-ready data products are created for every survey observation and released for public use after validation. I will give a brief summary of progress to date and a roadmap of improvements that the observatory would like to make. I will also outline options for larger-scale upgrades that aim to keep ASKAP at the forefront of radio astronomy into the SKA era. Ultimately, the case for an upgraded ASKAP will depend on the needs of the Australian astronomy community. Alongside direct community input and feedback, we hope to support an informed decision with prototype development that demonstrates emerging technology over the next few years.
[P049] “The Impact of ionisation Morphology and X-ray Heating on the Cosmological 21cm Skew Spectrum” – Jaiden Hue Cook
The cosmological 21cm signal offers a potential probe of the early Universe and the first ionizing sources. Current experiments probe the spatially-dependent variance (Gaussianity) of the signal through the power spectrum (PS). The signal however is expected to be highly non-Gaussian due to the complex topology of reionisation and X-ray heating. We investigate the non-Gaussianities of X-ray heating and reionisation, by calculating the skew spectrum (SS) of the 21cm signal using MERAXES, which couples a semi-analytic galaxy population with semi-numerical reionisation simulations. The SS is the cross-spectrum of the quadratic temperature brightness field with itself. We generate a set of seven simulations from z=30 to z=5, varying the halo mass threshold for hosting star-formation, the X-ray luminosity per star-formation rate, and the minimum X-ray energy escaping host galaxies. We find the SS is predominantly negative as a function of redshift, transitioning to positive towards the start of reionisation, and peaking during the midpoint of reionisation. We do not see a negative dip in the SS during reionisation, likely due to the specifics of modelling ionization sources. We normalise the SS by the PS during reionisation isolating the non-Gaussianities. We find a trough (k~0.1 Mpc-1) and peak (k~0.4-1Mpc-1) in the normalised SS during the mid to late periods of reionisation. These correlate to the ionization topology, and neutral islands in the IGM. We calculate the cosmic variance of the normalised SS, and find these features are detectable in the absence of foregrounds with the SKA_LOW.
[P104] “The Mimic in the (Hexagonal) Mirror: Using JWST Data to Form Spatially Resolved SEDs of EoR Analogous Galaxies.” – Samuel Colliver
The Epoch of Re-ionisation (EoR) stands as a vital era in cosmic evolution, marked by the birth of the first luminous sources alongside the ionisation of neutral Hydrogen in the intergalactic medium (IGM). Despite decades of research, a complete understanding of the EoR remains elusive. The MOSEL (Multi-Object Spectroscopic Emission Line) survey, aim to shed light on this epoch by identifying and studying galaxies analogous to EoR galaxies. These EoR analogues are chosen to have similar emission line equivalent width and star formation properties to the first galaxies, while providing better photo-metric sampling, as well as being brighter and larger enabling a detailed morphological analysis. We use the Hubble Space Telescope (HST), alongside the James Webb Space Telescope (JWST) data to construct spatially resolved SEDs (Spectral Energy Distribution) for these mimic galaxies. Through the SED fitting we identify where young stars are located in mimic galaxies, i.e., are they more centrally concentrated. This project will provide deeper understanding how first galaxies build-up their stellar mass.
[P075] “Deciphering Nature versus Nurture: An Analytical Investigation of Environmental Influences on Galaxies in the Local Cosmic Web” – Wesley Van Kempen
Environment has long been known to have an impact on the evolution of galaxies, but disentangling its impact from mass evolution requires the careful analysis of statistically significant samples. By implementing systematic improvements on previous studies, including cutting-edge visualisation to test and validate group-finding algorithms, we utilise a mass-complete sample to z < 0.1 comprised of spectroscopic measurements from prominent surveys such as the 2-degree Field Galaxy Redshift Survey (2dFGRS) and the Galaxy and Mass Assembly (GAMA) Survey. Bespoke Wide-Field Infrared Survey Explorer (WISE) photometry provides accurate measurements of stellar mass and star formation rates which provide the best possible description of the variation of galaxy properties as a function local environment. We highly optimised the identification of local (group) environment by training group finding methods on mock observations, providing us with highly robust galaxy groups over a contiguous 384 square degree area. The high, but varying, completeness of the spectroscopic redshifts helps inform how to maximise the spectroscopic redshift information from forthcoming surveys in the nearby Universe such as the 4MOST Hemisphere Survey. It also provides a benchmark for the aggregate star formation behaviour as a function of stellar mass for groups that will be observed as part of the HI surveys executed by the SKA and its Precursors MeerKAT and ASKAP.
[P061] “Abundance differences between dwarf galaxy streams and accreted stars” – Miles Pearson
I will present a comparison between the abundance patterns in accreted dwarf galaxies and dwarf galaxy streams. I have compiled data for accreted stars from public datasets including Gaia, APOGEE and GALAH, using dynamics to identify progenitors including Gaia-Sausage-Enceladus, Sagittarius, Sequoia, Kraken, and Thamnos. I have taken abundances from S5, Gaia, and APOGEE for stars in several dwarf galaxy streams. The abundance patterns in dwarf galaxies, particularly in iron-peak, alpha, and neutron-capture elements, can be used to infer information on galaxy mass, star formation history, and the state of the stellar population at the time of capture. The aim of this project is to track those factors from the oldest accretion events through to ongoing accretion in streams. This will help to build a clearer picture of the merger history of the Milky Way and provide an empirical baseline to compare against simulations of spiral galaxy formation.
[P101] “The circumgalactic medium in different group environments” – Antonia Fernández
Most galaxies live in group environments, where they undergo a more rapid evolution than isolated galaxies due to interactions and more rapid gas processing times. Therefore, studying the circumgalactic medium (CGM) of group environments is fundamental to understanding galaxy evolution. Unfortunately, most of the research about the CGM has been performed on galaxies that are located in isolated environments or poorly defined group environments, so the characteristics of the CGM in group environments remain uncertain. In this talk, I will present an analysis of the CGM of two galaxy groups in different stages of interaction: (1) a close pair of galaxies that do not show obvious signs of tidal interactions and (2) an actively merging pair of galaxies with evidence for a bridge of [OII] emission between the galaxies. I present Keck/KCWI observations of the galaxies and HST/COS spectra of a nearby quasar (30-80kpc away) to quantify the CGM in these environments. This analysis will include a thorough examination of the galaxy metallicities and kinematics compared to that of their CGM. I will also include a detailed description of the multiphase CGM surrounding these galaxy pairs, as probed by the background quasar, including the different processes that the gas is going through at different environments.
[P082] “Persistent gravitational radiation from glitching pulsars” – Thippayawis Cheunchitra
Pulsar glitches may be caused by the sudden unpinning and collective movement of vortices in the superfluid condensate inside the star, also known as vortex avalanches. The metastable vortex configuration between avalanches is nonaxisymmetric in general, producing a small but nonzero current quadrupole moment which generates persistent, quasi-monochromatic gravitational waves as the star rotates. In this work, we use an N-body simulation of vortex avalanches to calculate an empirical scaling of this current quadrupole, and extrapolate that scaling to estimate the characteristic wave strain for this mode of emission. We also develop analytic upper- and lower-bound characteristic wave strain, which corresponds to idealized regimes in vortex dynamics and bracket the empirical scaling. Such signal could provide insight into quantum mechanics of vortex in a regime inaccessible via terrestrial experiments.
[P043] “Understanding the link between dust geometry and star formation rate in galaxies” – Tania Ahmed
We investigate the link between dust obscuration and star formation rate (SFR) estimators using Halpha and radio luminosities. The ratio of SFRs estimated from radio and Halpha luminosities can be used as a probe of the degree of optically thick dust affecting Halpha. We explore this combining Evolutionary Map of the Universe (EMU) Early Science data in the Galaxy and Mass Assembly (GAMA) G23 field with the GAMA data by drawing on dust estimates using both Balmer decrement (BD) and the dust mass, demonstrating systematic underlying dependencies with the radio-to-H\alpha luminosity ratio. Defining two novel dust geometry metrics by combining the BD and dust mass, we establish how they relate to this luminosity ratio and other galaxy properties. We independently confirm the utility of these new metrics as a way to quantify dust geometry. We use this approach to establish an improved estimator for the Halpha SFR that accounts for optically thick dust. We also establish a strong correlation between specific star formation rate and the dust opacity and geometry in galaxies.
[P160] “Identifying variables and transients in ThunderKAT using Gaussian Processes” – Shih Ching Fu
A robust yet descriptive characterisation of light curves is essential for identifying interesting sources in large-scale sky surveys such as ThunderKAT. This challenge of finding satisfactory representations of light curves is confounded by data quality issues such as sparsity of data and irregular sampling, and by nuisance factors inherent in data collection. Furthermore, the wide diversity of sources captured by large-scale surveys requires any characterisation to be highly flexible yet not be unduly susceptible to overfitting. In this work we present a Gaussian process (GP) modelling approach to characterising light curves, as demonstrated on a dataset of 5131 radio light curves from the ThunderKAT survey. GPs offer a statistical representation that can overcome sparsity of data and offer statistically robust yet astrophysically meaningful interpretations to its fitted model parameters. We found that the distribution of the fitted amplitude hyperparameters can be used for distinguishing variable source candidates from amongst non-variables. Interestingly, there are distinct regions in the hyperparameter-space that further indicate a candidate’s propensity to be a transient or variable source. A judicious choice of GP kernel function explicitly accounted for the effects of survey properties, such as observation cadence, which can obscure proper source classification. A comparison is made with more traditional metrics for variability used in radio astronomy and this GP approach offered improved discriminatory power and interpretability.
[P189] “Crossing the Streams: The S5 Survey’s View of the Galactic Halo” – Daniel Zucker
Large galaxies like the Milky Way form hierarchically, with smaller systems merging and accreting to form increasingly massive structures. Evidence for this process can be found all around us: dynamically, as stellar overdensities in phase space in the nearby Galaxy; chemically, in the form of abundance patterns distinct from those of stars which formedin situwithin the Milky Way; and spatially, in the form of stellar streams and tidally disrupting satellites in the Galactic halo. This last domain – a halo dramatically criss-crossed by an abundance of stellar substructures – is the focus of the Southern Stellar Stream Spectroscopic Survey (S5), an Australian-led international collaboration using the AAT + AAOmega to study the streams and disrupting satellites surrounding the Milky Way. Its science goals include characterising the Galaxy’s accretion history and constraining the distribution of matter interior to stream orbits. Among the science results I will discuss are evidence for the influence of the LMC on halo stream orbits (and the Milky Way itself), the orbital properties of the stellar streams observed, and comparisons with simulation predictions for detectable streams and satellites. I will conclude with a look at the prospects of new facilities such as LSST and 4MOST for driving major advances in our understanding of how galaxies like the Milky Way grow.
[P135] “Characterising outflows using Mg II ultra-strong absorbers” – Antonia Fernández
The gas surrounding galaxies, also known as the circumgalactic medium (CGM), is a giant reservoir beleived to host 50% of the baryonic matter in the Universe. Unfortunately, the CGM is usually too diffuse to be studied in emission, so it is observed through absorption lines in background QSOs. It has been well studied that the absorption strength of the CGM decreases with distance from the centre of its host galaxy, however, there is a population of absorbers that seem to defy this notion: the Mg II ultra strong absorbers. These absorbers have a rest-frame equivalent width higher than 3 Å, independent of their impact parameter. Two hypotheses have arisen to explain these phenomena: (1) galaxy mergers produce them, or (2) they come from star-formation driven outflows. In this poster, I present a sample of five ultra-strong absorbers associated with star-forming galaxies. Using Keck/LRIS spectroscopy of both the host galaxies and their background quasars, I will look for outflows in the galaxies. I will also characterise these outflows and study their velocity gradients. This type of analysis has only been done once before in the literature and it will provide further insights into the nature of star-formation driven outflows.
[P192] “Lithium-rich giant stars: big data, new questions” – Sarah Martell
Around 1% of post-main sequence stars are observed to have more lithium in their atmospheres than is expected from standard stellar evolution, with some even above the Big Bang Nucleosynthesis level. Lithium is destroyed by nuclear fusion at a relatively low temperature, making these lithium-rich giants surprising observationally and difficult to explain theoretically. From studies using abundance data from large spectroscopic surveys like GALAH, Gaia-ESO and LAMOST and asteroseismic data from the Kepler and TESS satellites, we know that the likelihood for a star to be lithium-rich is higher if it has a higher metallicity or is in the helium core burning phase. We also know that some lithium-rich giants are rapidly rotating or show an infrared excess indicating dusty winds. I will discuss the results of recent ensemble studies of lithium-rich giants and discuss how a new, more precise catalogue of lithium abundances for GALAH will enable progress in this area.
[P108] “Using Transit Timing of Hot Jupiters to Search for Companion Planets” – Brendan McKee
Searching TESS data for TTVs in hot Jupiter systems should find more examples of planets whose orbits change due to one of these factors, including the possibility of establishing a rate at which they have companion planets. We have begun a systematic search of hot Jupiters observed by the TESS mission to identify potential companions. Here, I will highlight one example TOI-2818 b, the first hot Jupiter with TTVs identified in this campaign.
TOI-2818 b is a hot Jupiter orbiting a slightly evolved G-type star that shows transit timing variations (TTVs) suggestive of a decreasing orbital period. Over a 4-year TESS baseline, transits arrive ~8 minutes earlier than expected for a constant initial period. The implied orbital decay rate is too fast to be explained by tidal dissipation with a reasonable tidal quality factor. We use radial velocity measurements to rule out changes in light travel time from a distant companion as the cause. Apsidal precession due to tides requires impossible Love numbers to match the TTVs. The most likely possible cause of the TTVs is another short period planet. If the planet is in or near a mean motion resonance, it could produce large enough TTVs while remaining mostly hidden in the radial velocity and transit data. We conclude that a nearby planet is the most likely cause of the TTVs.
[P064] “A new approach to quantifying dust in galaxies” – Breanna Farley
I introduce a new approach to quantifying dust in galaxies by combining information from the Balmer decrement (BD) and the dust mass. While there is no explicit correlation between these two properties, they jointly probe different aspects of the dust present in galaxies. Two new parameters that link BD with dust mass are explored using star formation rate sensitive luminosities at several wavelengths (ultraviolet, Halpha, and far-infrared). Combining the BD and dust mass provides new metrics sensitive to the degree of optically thick dust affecting the short wavelength emission. These new parameters are demonstrated to be sensitive probes of the dust geometry in galaxies. Exploring them as a function of star formation rate shows that they support the “maximal foreground screen” model for dust in starburst galaxies. I also discuss the future potential of these new “dust geometry” parameters.
[P110] “Designing for Everyone: Introducing the new Data Central web app.” – Elizabeth Davies
Data Central has undergone a transformative redesign, prioritizing a truly user-centric experience. Our platform hosts diverse datasets, and each user interacts with them differently, driven by their scientific questions and objectives. That’s why we’ve reimagined how users access scientific data, making it more intuitive, efficient, and tailored to specific research needs. View a version 2 preview of our cutting-edge platform, where scientific data exploration meets extensive user customization and inclusive design. With a sleek and intuitive dashboard, we’ve seamlessly integrated an array of services, empowering scientific researchers to tailor their data experience like never before.
[P055] “The Kinematics of Milky Way Globular Clusters – An Insight into Stellar Halo Formation” – Finn Pal
Globular clusters (GCs) offer valuable insights into the formation and evolution of stellar halos within galaxies. Our study focuses on probing the kinematics of GCs to unravel the merger history contributing to the Milky Way’s stellar halo formation. We employ the Feeback in Realistic Environments (FIRE) simulations to investigate scenarios involving GCs originating from the same host galaxy being captured by Milky Way-mass galaxies. By calculating the timescale for the diffusion of GCs in kinematic space and assessing the range of their migration distances in kinematic space, we aim to investigate how the orbits of GCs change post accretion. This includes measurements of the total velocity, specific angular momentum, and specific total energy of the orbits. This will inform us of how the kinematics of GCs can be used to probe previous mergers and their contribution to the formation of stellar halos. Additionally, we conduct a comparative analysis between our simulations and observational data from the Gaia survey. This allows us to validate our simulations and investigate whether orbital trends seen in the simulation are also detectable within the kinematics of Milky Way GCs. This potentially offers new insights on the merger history of the Milky Way and the evolution of its stellar halo.
[P040] “Low radio frequency images of the southern Galactic plane for supernova remnant detection” – Silvia Mantovanini
There is an observed discrepancy of nearly 700 sources between theory and observation for the supernova remnants (SNRs) population in the Galactic plane. Although their mean radio spectral index of−0.5makes these objects brighter at low frequencies, we do not have the instrumental capabilities to detect the olderand fainter samples of sources.
We combined data collected by two surveys of the Murchison Widefield Array to obtain a deeper image of the plane. The wide field of view and the observing band (72–231 MHz) make this interferometer a useful resource in detecting radio emission from SNRs, that are brighter in this frequency range. The image obtained represents a unique example of combination between high resolution and sensitivity to all spatial scales (45″−15◦), achieved by the union of a short-baseline survey which resolve large scale structures, with a long-baseline survey which capture the fine details of smaller scales highly decreasing the noise level.The image covers a region of the Galactic plane within 240◦< l <50◦and|b|<10◦with an RMS noise varying from 10 to 2 mJy/beam across the observing band.
Thanks to the wide band, we will discriminate the contribution of thermal and synchrotron emissions and investigate the effects of free-free absorption either due to the presence of unshocked ejecta inside the shell or interactions with the surrounding environment outside the remnant.
[P072] “MAUVE: Tracking the influence of the environment on the gas-star formation cycle of cluster galaxies during infall” – Luca Cortese
I will present the first results from the MAUVE (MUSE and ALMA Unveiling the Virgo Environment) survey, a multi-wavelength observational campaign combining an Australian-led VLT/MUSE large program, ALMA and HI observations of 40 galaxies in the Virgo cluster aimed at understanding the environmental impacts on the gas-star formation cycle in cluster galaxies during their infall. These data are allowing us to probe the distributions and kinematics of stars, ionized and molecular gas over the full extent of the inner galactic disks, at scales of a few hundred of parsecs, making it possible to investigate the link between cold gas and star formation when and where environmental processes are at play. Excitingly, these observations are starting to reveal unexpected cases of star formation driven outflows even in ram-pressure stripped and HI deficient galaxies, as well as providing new insights into how star formation proceeds after first pericentre passage. While still at the early stages, MAUVE is showing how outflows may play an important role in the full quenching of the star formation and remind us how a multi-phase mapping of the interstellar medium is critical to fully unveil the physical processes driving. the star formation cycle of galaxies.
[P176] “Hunting for ionised gas outflows in Virgo galaxies with MAUVE” – Amy Attwater
How star formation ceases in galaxies is an ongoing open question in galaxy evolution. As stars form out of cold gas, the physical mechanisms that remove cold gas from galaxies will affect their star formation. Gas outflows, where large amounts of gas can be ejected via nuclear activity or supernova explosions, are one of these mechanisms, but there is much that we still do not know as they require high resolution observations, making suitable targets rare.
The ongoing VLT/MUSE large program MAUVE (MUSE and ALMA Unveiling the Virgo Environment) is uncovering complex structures and kinematics of the ionised gas indicative of stellar feedback-driven outflows. To isolate and characterise the outflows we are using a three-dimensional kinematic approach, which consists in modelling the underlying regular velocity field of these galaxies and subtracting it from the observed data, leaving the outflowing gas as residual.
In this talk, I will present preliminary results of this modelling process for a couple of MAUVE galaxies, including one with a central bar and a large-scale, ionised gas outflow. By isolating these outflows, we can characterise their geometry and velocity, clarifying their role in suppressing star formation.
[P059] “Measuring the intracluster light fraction using machine learning” – Louisa Canepa
The intracluster light (ICL) is an important tracer of a galaxy cluster’s history and past interactions. Up to now, only small samples of ICL have been studied due to its very low surface brightness, the difficulties in comparing measurement methods, and the high level of manual involvement needed for most measurements. To process the amount of data expected from upcoming imaging surveys like Euclid and the Vera C. Rubin Observtory’s Legacy Survey of Space and Time (LSST), we need fully automated and fast methods to make these measurements. In this talk, I will present our work developing a machine learning model that can predict the ICL fraction in cluster images from the Hyper Suprime-Cam Subaru Strategic Program. I will show that this model has been able to effectively learn this task even with very few real data samples, using transfer learning from ICL fractions in artificially generated images. I will describe the methods we use that could be useful for similar machine learning applications in astronomy, and discuss the potential applications of this model with particular focus on upcoming large surveys like LSST.
[P006] “E-XQR-30: The early chemical enrichment and CGM reionization” – Alma Sebastian [R]
Metals play an important role in star formation activity in galaxies across different epochs. These heavy elements produced through stellar nucleosynthesis processes are expelled from the galaxies to the surrounding circumgalactic (CGM) and intergalactic media (IGM) through various feedback mechanisms such as galactic winds and supernovae. Obtaining a census of metals in the CGM across cosmic time thereby provides an independent measure of the global stellar production and galactic baryon cycle in different epochs. Here, I present my results on the comoving line density (/) of intervening absorbers such as Mg II, C II and O I across redshift ranging from ∼ 2 to 6 using the E-XQR-30 (The Extended Ultimate XSHOOTER Legacy Survey of Quasars at ~5.8 − 6.6) metal absorber catalog prepared using high quality spectra from 42 bright quasars using an ESO-VLT Large Program. The improved resolution and sensitivity of E-XQR-30 have enabled us to calculate the first ever number density statistics of a large population of 131 weak intervening Mg II (with an equivalent width of < 0.3Å) systems at > 2. Overall, our results indicate that there has been significant enrichment of the CGM mostly through core-collapse supernovae from the tail end of the Epoch of Reionization (EoR) to the cosmic noon era. In addition, our results favour a patchy reionization model with a weak ionising radiation existing towards z < 5.7.
[P122] “Self-introduction: Dr. Larissa Markwardt – New Research Fellow at the University of Auckland” – Larissa Markwardt
My name is Dr. Larissa Markwardt, and I recently started as a Research Fellow in the Department of Physics at the University of Auckland. I’m an observer with experience primarily in optical and near-IR data.I am broadly interested our Solar System, transient objects, and using computers to solve astronomy problems. I recently received my PhD from the University of Michigan, where my thesis was focused on Trojan asteroids (especially Earth’s and Neptune’s). Over the next few years, I will be working on discovering and studying the faintest Mars Trojans to date, which will advance our understanding of Martian formation and history.
[P016] “Updates from the Australian SKA Regional Centre (AusSRC)” – Karen Lee-Waddell
The Australian SKA Regional Centre (AusSRC) is part of an international computing and data delivery network that will enable ground-breaking science by providing the connection between the SKA telescopes and the science community. Currently, AusSRC is working with SKA precursors, primarily ASKAP and the MWA, to test and develop scalable data analysis strategies and automated workflows that can eventually be applied to data from the SKA telescopes. We are also part of the increasing effort to prototype various aspects of the international SRC Network (SRCNet), such as testing data distribution and archiving frameworks, establishing operational requirements and pipelines, and building user interfaces. I will provide an update on our progress and an overview of how the AusSRC is facilitating the scientific output of the SKA research community.
[P018] “Each Station is as Unique as a Snowflake — The Consequences of Assuming Uniformity for Epoch of Reionization Science” – Aman Chokshi
All-sky satellite measurements of Murchison Widefield Array beams reveal significant asymmetric sidelobe distortions at an ~10% level, attributed to a range of environmental effects. In this talk I present the experiment used to carry out satellite beam measurements, and the Bayesian MCMC framework developed to incorporate these satellite measurements into a simulation test-bed to understand and propagate the effects of distorted beams on Epoch of Reionization (EoR) Science. I demonstrate how mismatches between realistically deformed beams and the perfect beam assumed during calibration lead to unavoidable spectral contamination between 100-1000 times brighter than the expected EoR signal. I also outline methods which will enable next-generation telescopes such as the Square Kilometre Array to implement parallel and affordable beam monitoring systems, facilitating the highest fidelity science outputs.
[P103] “Identifying Globular Clusters in Spiral Galaxies Using High-Resolution Spectroscopy from the GECKOS Survey” – Zahra Aliakbarzadeh
Globular clusters (GCs) serve as critical tools for understanding the formation and evolution of galaxies. Their ancient origins and broad distribution within galactic halos make them particularly valuable for studying the structure of spiral galaxies. This presentation outlines a new approach to identifying GCs in spiral galaxies through the GECKOS Survey. This MUSE program targets 35 edge-on Milky Way-like galaxies in the local Universe. Utilising deep (S/N> 40 at μ = 23.5 mag/arcsec²) and high spatial resolution (<200 pc) spectroscopic data, our methodology focuses on the photometric and spectroscopic analysis requiredto reliably identify point sources as bona fide GCs. I will discuss the criteria and techniques employed to distinguish these clusters against the complex backgrounds of their host galaxies. Additionally, the presentation will highlight the challenges and solutions in confirming GC candidates in environments dominated by the light of spiral galaxies. By cataloguing these GCs, we aim to enrich our understanding of their distribution and properties compared to those observed in the Milky Way, thus providing new insights into their broader galactic contexts.
[P063] “Searching for outflows in the extraplanar regions of edge-on galaxies” – Rory Elliott
There is a theoretical consensus that galactic winds/outflows are the dominant mechanism for regulating star formation and mass growth in galaxies. There is, however, no agreed-upon model describing the energetics of how outflows launch and maintain material outside the galactic disk . Moreover, we do not know how universally applicable the current models of outflows are, as they are primarily based on the nearest outflowing systems like M82. Historic limitations to sensitivity have made resolved studies of outflows uncommon, and typically limited to individual targets. The GECKOS project is an Australian lead MUSE LP that studies 35 edge-on galaxies, of which ⅔ are star-forming systems. GECKOS features extremely deep observations of ionized gas in galaxies, and is thus ideal for studying the resolved properties of galactic winds and outflows. In my work, I analyse the extraplanar gas emission from the first 9 galaxies that have been fully observed and reduced in the GECKOS sample. I use emission line ratios and gas kinematics to identify regions of each galaxy’s wind material that are likely impacted by shocks, as well as those dominated by photoionization. I will show that, in the strong starbursts, these findings are consistent with expectations of the multiphase biconical outflow model that is frequently used to describe winds. These results have implications for how outflows can be implemented into galaxy evolution models. These results also demonstrate the power of the GECKOS data set.
[P054] “Carbon and Lithium Depletion in Red Giant Stars” – Joseph Samuel
With the emergence of asteroseismology, an entirely new method of finding stellar masses has become available and as asteroseismology progresses, more and more stars are being characterised in surveys. I will be presenting work that compares the rate of deep mixing in red giant branch stars across mass and metallicity. The aim is to improve our current understanding of mixing processes within red giant stars using both spectroscopic and asteroseismic data. To facilitate this, I estimate masses using machine learning and determine the deep mixing rate from carbon and lithium abundances. This allows us to study this phenomenon across a larger parameter space than was previously possible. This will provide insights into the mechanisms for deep mixing and whether any of our current theoretical models for the processes line up with reality, whether it be rotational mixing, magnetic mixing, thermohaline mixing or some combination of these.
[P182] “Searching for Globular Cluster Escapees” – Nina Kesby
‘Second generation’ stars in globular clusters are characterised by unique light element anticorrelations in their chemistry, with enhancement in N, Na and Al but depletion in C, O and Mg/Si. Stars with globular cluster-like chemical signatures have been previously found in the Milky Way halo, as expected given the many gravitational interactions globular clusters undergo. In this project we aim to find more GC-like stars in the halo using updated GALAH data. We take two separate approaches: a straightforward selection based on high N and Na (and possibly Al) abundances, and using a data-driven clustering algorithm in chemical space, to determine whether any groups arise with globular cluster-like anticorrelations. In preliminary analysis we find that the statistically ideal number of chemical groups in the halo is 7-9. We are continuing to tune the clustering approach and investigate the features of each group, comparing to known chemical characteristics of the halo and features of globular cluster stars. The process by which globular clusters develop these abundance anticorrelations is unknown, as each scenario proposed has significant flaws relative to the observational data. The results of this project will provide better limits for the number of escaped second generation globular cluster stars in the halo, an important parameter for understanding the formation and history of globular clusters.
[P097] “50-250 MHz census of known pulsars with SKA-low prototype station” – Pratik Kumar
Pulsar observations at low frequencies are providing new insights into our understanding of the interstellar medium, constraints on ionospheric electron density, solar wind properties, and turnover in pulsar spectra at low frequencies. Although low-frequency pulsar observations have improved over the last decade, continuous monitoring remains challenging due to the associated high data volumes, especially in the case of offline beamforming instruments. This problem becomes more manageable with the real-time beamforming capabilities of the Engineering Development Array (EDA2), which is a SKA-low prototype station. Here we present a census of ~120 known pulsars detected by EDA2, at the lowest frequencies, to study the turnover in spectra while preparing for a monitoring campaign over a long time to study other phenomena as mentioned above.
[P126] “The earliest radio emission from gamma-ray bursts and gravitational wave events” – Gemma Anderson
The very earliest moments following a gamma-ray burst (GRB) or gravitational wave (GW) event is an underexplored regime at radio wavelengths. For this talk, I will provide a review of the scientific predictions and earliest detections of radio emission from such transients with a focus on results using Australian radio telescopes. The Murchison Widefield Array (MWA) and Australia Telescope Compact Array (ATCA) are capable of automatically responding to transient alerts using rapid-response observing systems that can have the telescopes on target on second to minute timescales. Such observations help to unify our understanding of relativistic outflows by probing central engines, jet composition, and host environments.
Using MWA, we seek to ascertain whether merging binary neutron stars (short GRBs and GWs) or massive stellar collapse (long GRBs) could produce supramassive neutron star remnants and be progenitors to some fast radio bursts (FRBs). The MWA response time of <10s can probe for FRB-like signals predicted at the time of merger, and I will outline the observing strategy for the current LIGO-Virgo-KAGRA O4 observing run.
Rapid ATCA observations on a long GRB have resulted in the detection of an unexpected radio flare likely caused by interstellar scintillation, placing the earliest size constraint on a GRB blast wave. We have also obtained the earliest radio detections of two short GRB, one of which shows evidence of a prolonged engine from a supramassive neutron star remnant. These results have motivated a large ATCA observing program of >1000 hours over 3yrs to trigger on all GRBs.
[P130] “Breaking the Warm and Cold Dark Matter Degeneracy; A love story” – Adam Ussing
Cold dark matter models explain the large-scale universe to a high degree of accuracy, but tensions with observations persist. Warm dark matter hasbeen proposedas an alternative to cold dark matter to solve tensions.To test this weused cold and warm dark matter simulations with different stellar physics prescriptionsanduseddust as our metric to probe the underlying dark matter model from an observational standpoint.
[P078] “The GLINT interferometer: Pathfinding the technology for next-generation high-contrast imaging” – Eckhart Spalding
GLINT is an interferometer downstream of the SCExAO extreme-adaptive-optics system at the Subaru Telescope (Hawaii, USA), and is a pathfinder instrument for high-contrast imaging of circumstellar environments in the near infrared with miniaturized “photonic” optics. GLINT is effectively a testbed for more stable, compact, and modular instruments for the era of telescopes of 30m-class or larger. The instrument works by directing light from the Subaru telescope into specially shaped, ultrafast-laser-inscribed waveguides inside a glass chip which weighs just a few grams, and then directs the interfered outputs onto a detector. The “nulled” output has had the light from the host star subtracted away, and passes only off-axis light to the detector. GLINT has already successfully measured stellar diameters of ~10s milliarcsec, below lambda/D, and is now undergoing a sensitivity upgrade with a new chip featuring waveguide modifications for more achromaticity and for phase information to enable phase stabilization. Here we provide an overview of the motivations for the GLINT project, and report on the design, installation, and current status. We finish with ideas for future directions of this project, which will involve more advanced chips and possible detector upgrades, as well as provide context for the current stage of the GLINT project as a stepping stone to photonic nulling instruments at other and future facilities.
[P187] “Pre-main sequence stars in the time domain: insights from high-precision and multi-wavelength photometry” – Laura Venuti
Photometric variability is a defining feature of young stellar objects (YSOs), and it provides a unique observational tool to reconstruct the physical conditions at the stellar surface and in the inner circumstellar disk regions for large samples of young stars. YSO variability is a panchromatic phenomenon, with characteristic signatures from the ultraviolet to the infrared that reflect the dynamics and interplay of distinct physical processes, from stellar magnetic activity to mass accretion and star-inner disk interaction. Thanks to dedicated space-borne surveys conducted with CoRoT, Kepler/K2, and TESS, and to coordinated observational efforts from the ground, accurate time domain data for hundreds of young stars are now available for virtually every stage of protoplanetary disk lifetimes, across different stellar mass regimes from cool stars and beyond. In this talk, I will discuss the insights provided by those campaigns into the time evolution of inner disks around young stars, and what these observations teach us regarding the stellar and circumstellar dynamics as a function of stellar mass and environmental conditions, focusing in particular on the Lagoon Nebula star-forming region.
[P116] “Fast scintillating quasars as a probe of unseen interstellar structures” – Hayley Bignall
Compact (≲1 mas), centimetre-wave radio sources twinkle, as a result of radio wave scattering by electron density inhomogeneities in our Galaxy. The twinkling phenomenon, known as interstellar scintillation (ISS), can occur on a range of timescales, depending on the scattering strength and distance to the scattering material, as well as the relative velocity between observer and scintillation pattern. In detailed studies, scintillation of both pulsars and AGN is usually well described by scattering in discrete, “thin” screens with highly anisotropic (effectively 1-D) microstructure. New theoretical developments are being made which could lead to an understanding of the origin of these scattering screens.
The ubiquity of “scintillation arcs” observed in pulsar secondary spectra implies that such discrete scattering structures, with filamentary microstructure, must exist throughout the Galaxy. It is plausible that a large fraction of baryons may reside in the associated structures.
Large amplitude, intra-hour variability (IHV) of AGN due to ISS is rare, as a “screen” must be within ~10 pc of the observer to cause fast ISS. We are taking advantage of ASKAP’s wide field of view to find the fast scintillators, which so far appear to be highly clustered. Multi-epoch follow-up with various facilities, including ATCA and MeerKAT, allows us to measure annual cycles in the timescale of ISS. Annual cycles provide information on the structure and dynamics of the nearby scattering screens, allowing crucial tests of the new theoretical models.
[P123] “Uncovering neutron star mergers” – Cassidy Mihalenko
Gamma ray bursts (GRBs) are classified into long and short. Long GRBs have been long associated with supernovae (SNe) progenitors, with many observed coincident with SNe or with SNe features in the spectra or light curve. The joint detection of gravitational waves and a short gamma ray burst (GRB) of GW170817/GRB170817A provided the first direct evidence that neutron star (NS) mergers are the progenitors of at least some short GRBs. Multi-wavelength follow-up observations of the afterglow provided the first confident, well sample kilonova (KN) observations, a radioactively powered transient produced by the neutron rich environment of NS mergers.
However, there are some GRBs that do not cleanly fit into the typical long and short classification. Short GRBs with extended emission after the main burst that don’t have entirely typical short properties, possibly indicating a different progenitor or observational effects. Additionally, a few long GRBs have recently been observed to have potential KN emission, a feature of NS mergers. These have some observational properties typical of long GRBs, but some that are typical of shorts.
My research is investigating the optical observational properties of any possible KN and these unusual GRBs to understand their progenitors, the properties of GRBs and afterglows produced by NS mergers, and constrain KN models in optical afterglows. This will be used to expand the sample of observed NS mergers, which will be invaluable in probing the properties of GRBs, compact objects, and provide constraints on cosmological parameters, including the Hubble constant.
[P112] “The salty winds of intermediate-mass AGB stars” – Taissa Danilovich
Asymptotic giant branch (AGB) stars are a late evolutionary stage of low- and intermediate-mass stars like our Sun. During this phase, stars throw off their outer layers through stellar winds rich in molecules and dust. Previous studies of the molecules in AGB stellar winds found that several molecules have strong dependences on the mass-loss rate or the density of the wind, showing either different abundances or distributions with wind density. To explore this phenomenon further, we examined the molecular emission around two of the highest mass-loss rate AGB stars that have been observed with ALMA. In addition to several expected molecules, we also found a large number of emission lines coming from salt molecules. I will discuss these findings and their implications for the chemistry and physics of the circumstellar environments of these stars.
[P067] “The dynamical origin of the Hercules stream” – Harry Li
The Hercules stream is a kinematic anomaly pattern of stars observed in the solar neighbourhood (SNd). Modern big data surveys like Gaia, APOGEE, and GALAH have revealed the distinct metallicity and kinematics features of Hercules stars, and studies have supported their identity as a moving group. However, the origin of this population is still a topic of debate, and the explicit mechanism of moving groups is only vaguely related to bar resonances. A model is proposed based on analytic potentials and compared with observational data from Gaia for validation. From numerical simulations, lower energy quasi-periodic orbits (QPOs) trapped around fast-rotating periodic orbits around the L4 Lagrange point of the Galaxy bar minor axis can reach SNd, and when observed in SNd, they populate the kinematics region where Hercules structure is found.
[P089] “Using FRBs to explore the cosmic baryon distribution” – Jordan Hoffmann
Fast radio bursts (FRBs) are millisecond duration highly energetic radio bursts of unknown origins. They are known to be extragalactic and hence studying their propagation effects allows one to use them as cosmological probes. In particular, the dispersion measure (DM) traces the number of free charges along the line of sight. Comparing the number of baryons with the distance to the burst in a redshift-dispersion measure (z-DM) analysis then allows FRBs to trace cosmological baryon distributions. We additionally fit FRB population parameters as part of this analysis and find evidence for a minimum FRB energy which could shed light on the currently unknown emission mechanism. We provide our latest estimates on H0, the gas content of the Milky Way halo and FRB population parameters.
[P154] “Probing Gravitational Wave Merger Physics Through Radio Observations: Insights from ASKAP” – Ashna Gulati
The electromagnetic radiation accompanying GW170817, allowed the binary-neutron-star merger physics to be studied in great detail. Generation of electromagnetic radiation in a compact binary system requires the presence of a neutron-star in the compact system to provide tidally disrupted material that hyper-accretes onto the nascent black hole. However, some theories propose electromagnetic radiation to be plausible in a binary-black-hole merger, wherein jet power can be fueled by pre-existing residual debris surrounding the compact binary system or from electromagnetic sources that enhance the magnetic fields.
In this talk, I will present results from a study on the constraints we can place on GW merger physics through using radio data from widefield surveys conducted with the Australian SKA Pathfinder. We used data from four epochs of the Rapid ASKAP Continuum Survey, covering the entire southern sky, to inspect compact binary merger localizations observed during the LIGO-Virgo O1, O2, and O3 observing runs. Our investigation focused on twelve events (published in GWTC-1, GWTC-2, and GWTC-3) within a 90% posterior localisation limit of 150 deg2 and a >=99% probability of being of astrophysical origin, to identify potential radio counterparts. I will discuss our search for late-time radio counterparts at frequencies ranging from 0.9 to 1.6 GHz. I will also discuss the constraints we can put on the inclination angle and other physical properties of these events. Finally, I will discuss the anticipated explosion energies, inclination angles, and circum-merger densities that such a search is useful for in comparison to other counterpart multi-wavelength studies.
[P164] “The Largest Continuous Black Hole Jet Ever Seen in our Galaxy” – Callan Wood
High angular resolution observations of the relativistic jets launched by accreting stellar-mass black holes in Galactic X-ray binaries are essential for understanding the jet launching mechanism and the connection between jet launching and the accretion inflow. Unlike many nearby AGN, the continuous outflowing jets of X-ray binaries are rarely resolved and instead appear in images as compact radio sources. This limits our ability to obtain model-independent probes of their properties and connect these to observations of the accretion flow. During its recent bright outburst, we observed the candidate black hole low-mass X-ray binary Swift J1727.8-1613 with three VLBI arrays, including Australia’s Long Baseline Array. At the beginning of the outburst, our images showed a bright core and a large, two-sided, asymmetrical, resolved jet. Depending on the distance to the source and inclination of the jet axis, the physical jet likely extended beyond 100 AU in length. Our images show the most well-resolved continuous X-ray binary jet, and possibly the most physically extended continuous jet ever observed in an X-ray binary. Using our images, we were able to put constraints on the intrinsic speed and inclination of the jet. In later observations, the continuous jet faded and became less extended, and transient discrete jet ejecta were launched, accompanied by bright X-ray and radio flaring. To analyse these data, we developed and implemented new techniques that can account for the rapid intra-observational variability and motion of these transient jets, similar to the techniques developed by the Event Horizon Telescope collaboration.
[P118] “Shedding light of Black Hole mergres in Active Galactic Nuclear (AGN) discs” – Evgeni Grishin
The database of black hole (BH) gravitational-wave mergers is increasing with over a hundred events, and studying their astrophysical origins opens up a new window to the universe. Scenarios range from the evolution of a massive binary in isolation to chaotic interactions in dense environments. The centres of galaxies are a special environment where the BH can merge several times without escaping due to the massive gravitational pull of the Supermassive BH in the centre. Some galaxies also have a massive accretion disc of gas, which makes the galaxyextremely luminous and known as Active Galactic Nuclei (AGN).
The interaction of stellar mass BH and the AGN disc makes the BHs migrate in and out, depending on the properties of the disc. There are special locations where the extra torques vanish and a stable equilibrium forms – the migration trap. BH tend to accumulate in migration traps, which in turn increases the chances for close encounters in its vicinity. We study additional thermal effects wherethe stellar-mass BH accretes and heats the remaining gas, which affects the total torque. In some cases, thermal effects shift the migration trap to a more distant location, or remove it entirely. We find that AGNs above a critical luminosity of about 10^45 ergs s^-1 cannot form traps, and lower luminosity AGN will have more distant traps. We discuss the implications on AGN feedback, BH merger rates and properties in the context of gravitational-wave astronomy and present the ongoing and future research directions.
[P022] “Probing dark matter using gravitational waves from galactic binary black holes and LISA” – Sohan Ghodla
Binary black holes (BBHs) living in dense dark matter environments (e.g., close to the galactic center) will capture the surrounding dark matter during their evolution. The changing mass of the BBH will introduce an anomaly in its emitted gravitational wave phase compared to when the binary is assumed to live in a vacuum. Depending on the properties of the surrounding dark matter and the location of the BBH (w.r.t. the center of our Galaxy), in this talk, I will show that LISA may be able to detect such an anomaly making these BBHs (if detected) an excellent indirect probe of their dark matter surrounding.
[P052] “Beyond the Mass Step: Improving the Hubble Diagram with an [O II] Correction to SN Ia Light Curves” – Bailey Martin
For the last decade, SN Ia light-curves have been corrected for the mass step, a phenomenon by which more massive galaxies host SNe Ia that are systematically brighter after standard light-curve corrections. We have obtained WiFeS IFU spectra of over 100 SN Ia host galaxies, and found that there is an interconnected system of correlations between SN Ia luminosities and host properties that is not accounted for by a mass-step correction. Instead, we find that correcting for the [O II] equivalent width – a tracer of sSFR – accounts for the system of correlations we see, and reduces the scatter in the Hubble diagram to a greater extent than a mass step correction. The availability of the [O II] feature in optical spectra out to z~1.5 makes it an excellent option for the correction of SN Ia light-curves.
[P131] “ESO Downloader: a proposal-focused download tool and Python API for accessing proprietary and public data from the ESO Archive.” – James Tocknell
Originally created for the GECKOS and MAUVE teams, the eso-downloader Python package provides a simple CLI interface to the ESO archive to download entire proposals from the ESO archives. It also provides Pythonic wrappers around each of the components of the download process (such as getting the token to access proprietary data, finding the OBs for a proposal, finding the science frames for an OB, getting the calibrations for a science frame, and checking the quality of an OB), allowing you to download the data you need as part of your data reduction pipeline. It is available on PyPI, and community contributions are welcomed at https://dev.aao.org.au/adacs/eso-downloader [https://dev.aao.org.au/adacs/eso-downloader].
[P114] “Searching for gamma-ray emission from flaring stars” – Sam He
Given that solar flares contain gamma-ray (GeV) emission, it is reasonable to anticipate similar mechanisms occurring within stellar flares on other stars. However, apart from the Sun, the only confirmed isolated main sequence star is TVLM 513-46546, a rapidly rotating red dwarf star whose GeV signal is confirmed using phase-folding techniques. Dwarf stars are excellent candidates for GeV emission because they are more magnetically active than the Sun. The detection of TVLM 513-46546 suggests GeV emission from dwarf stars should be universal even though they are hard to detect. In this work, we utilised 15 years of Fermi Gamma-ray Space Telescope data to study radio and optical flaring stars from the most up-to-date catalogues. We search for GeV emission from over 300 flaring stars within 50 pc of the Sun when they flare. Analyses of individual stars do not exhibit new tentative candidates. Hence the population of flaring stars are spatially stacked to improve the sensitivity and provide constraints on the properties of the flaring population. Even though stacking does not return a detection, we have indicated the power law index to be peaking around -2, and retrieved a sensitive flux upper limit. This work gives insights into the properties of high-energy particles produced through these extreme stellar activities. If proven universal, these high-energy events can diminish the chances of finding habitable planets.
[P136] “Coming Soon: Data Central’s Jupyterhub will allow you to bring your code to Australia’s optical data” – James Tocknell
Jupyterhub is a platform that provides notebooks, unix shells and even an X11 desktop within the browser. Data Central is combing Jupyterhub with its existing archives to allow astronomers to use their existing tools, like Python, R and even DS9 (or IRAF!) to interact with all the data hosted at Data Central. You won’t need to download anything, and you will be able to upload your own data and code! This system will also allow you to reduce your ESO observations, with pre-configured environment with the ESO pipelines already installed.
[P150] “Imaging pulsar census of the Galactic Plane using MWA VCS data” – Susmita Sett
Pulsars play a crucial role in exploring a wide range of physics and astrophysics, such as probing dense-matter physics and testing strong-field gravity. Traditional pulsar surveys have mostly used time-domain periodicity searches, but these methods can be hindered by scattering, eclipses, and orbital motion, especially at low radio frequencies. In contrast, image domain searches for pulsars are more effective, enabling discoveries in the parameter space unreachable by traditional methods. A pipeline has been developed to form 1-second full Stokes images from high-time-resolution data from the Murchison Widefield Array (MWA). This led to the exploration of image-based techniques for identifying new pulsar candidates.
In this talk, I will describe a low-frequency image-based pulsar census of the Galactic Plane (GP) with the MWA focused on detecting the known pulsars in the observed region of the sky using both image-based and beamformed methods. This effort led to our detection of known pulsars, with some being detected for the first time at low-frequency. The continuum flux densities of the pulsars detected in our image-based GP survey are significantly more reliable than the timing flux densities and therefore offer an additional benefit as flux densities are not readily available or are unreliable for many known pulsars at low frequencies. Therefore, imaging is an effective approach for discovering new pulsars in less-explored regions of the DM space and improving the spectral modelling of the known detected pulsars. Upcoming facilities like SKA-Low will enhance the success of such image-based pulsar searches and aid in identifying new pulsars.
[P037] “Radio-Loud Analogues of Little Red Dots or Ultra-High-Redshift Radio Galaxies?” – Alexander Hedge
Some of the most complex galaxy over-densities and massive, obscured AGN in the distant Universe have been pinpointed by bright radio sources in the form of high-redshift radio galaxies (2
[P168] “Estimating accurate reddening values of LAMOST M dwarfs” – Han Shen
Interstellar dust is an important part of the Milky Way. Dust absorbs and scatters the starlight that passes through, causing extinction and reddening. Dust plays an essential role in the formation of molecular clouds and stars. About 30% of the radiation of our universe comes from the interstellar dust. M dwarfs are the stars of low masses and faint magnitudes. They serve as excellent tracers for the study of the distribution and properties of dust in the Solar Neighbourhood. We aim to obtain accurate reddening values of M dwarfs in the Solar Neighbourhood. Based on the dwarf catalogue from LAMOST DR8, combining data from Gaia eDR3 and 2MASS, we obtain a sample of 661,532 M dwarf stars. We use random forest regression to obtain intrinsic colours of stars. We select stars with high signal-to-noise ratio and locating at low extinction region as the training sample. Twelve parameters including the spectral indices are set as input parameters. We train the random forest models for two intrinsic colours of(GBP-GRP)0and(G -KS)0of M dwarfs. The models are applied to obtained their accurate reddening values. We have explored the reddening distribution in the Solar Neighbourhood. The internal statistical errors of the resultant reddening values in our sample is 0.03 mag, which indicates that our results are robust. We compared our resulted reddening values with previous works, which are of good agreements. The resultant catalogue containing a large number of M dwarfs will benefit further studies in related field.
[P028] “The Era of Big Mock Data: Understanding Galaxies through Simulation-based Inference” – Connor Bottrell
The next generation of galaxy astronomy will be shaped by the unprecedented output from instruments like the Square Kilometer Array, Euclid space telescope, and Rubin Observatory. Most importantly, data from these facilities will be gauntlets through which competing models of galaxy formation will be tested. Running these tests demands an apples-to-apples approach that is efficient, sensitive, and goes beyond reductive scaling relations. In this talk, I will show that large samples of realistic, multi-wavelength mock images made from structures formed in cosmological simulations make it possible to (1) compare simulated universes to ours; (2) map observables to unobservables and (3) port these mappings to the real Universe. I will first show that deep contrastive learning supports comparisons of mocks and observations with minimal information loss. Next, I will show that simulation-based inference models can be trained on simple, image-based observables to significantly reduce the intrinsic scatter in key relations, such as the stellar-to-halo mass relation. Lastly, I will show that simulation-trained deep generative models can be used uncover substructures buried in noisy and blurry images across very different domains — from galaxies to planetary disks.
[P158] “Simple Spectral Access for IFS data: search through and download Australian IFS surveys with ease!” – James Tocknell
Data Central is expanding its existing Virtual Observatory Simple Spectra Access service to also provide access to Integral Field Spectra (IFS) surveys like SAMI. You’ll now be able to use tools like TOPCAT and pyvo to filter through the numerous cubes, maps and 1D spectra from IFS surveys, and download only those files that you need for your science.
[P151] “Constraints on viscosity of accretion disks using LSST” – Susmita Sett
The LSST survey by Vera C. Rubin observatory will provide unprecedented coverage of transients that enables a detailed exploration of physics in energetic phenomena. One of the key classes of objects this survey will shine light on will be accreting black holes and neutron stars. I will present our work on detailed constraints we get on accretion disk physics from the LSST.
[P087] “Parameter estimation for a two-component neutron star model with a Kalman filter.” – Nicholas O’Neill
Pulsar timing noise is the stochastic deviation of the pulse arrival times of a pulsar away from their long term trend. In the standard two-component crust-superfluid neutron-star model, timing noise can be explained as the perturbation of the two components by irregular torques. Interactions between the crust and superfluid cause these perturbations to decay exponentially with a characteristic relaxation time scale. This research uses a Kalman filter to track the pulsar rotation frequency over time and calculate a probability distribution for the parameters of the two-component pulsar model. Our method is reliable on simulated data, which we show through individual and large-scale Monte Carlo tests. We also show a representative example on publicly available data from a real pulsar, where we test the two-component model and use it to efficiently measure physical properties of the star, including the relaxation time scale. Our measurements of the properties of neutron stars may provide insight into their internal structure and also provide evidence for or against the two-component model.
[P096] “PSR J1631–4721: The Discovery of a High DM Pulsar Associated with the Supernova Remnant G336.7+0.5” – Adeel Ahmad
Detecting a pulsar in it’s parent supernova remnant (SNR) or resulting pulsar wind nebula (PWN) is crucial for unravelling its formation history and pulsar wind dynamics, yet the association with a radio pulsar is observed only with small fraction of known SNRs. Recent advancements in radio continuum surveys enable the identification of compact objects within the SNRs, facilitating the targetted searches for radio pulsars. In this paper, we report the discovery of a young pulsar, J1631-4721, associated with Galactic SNR G336.7+0.5, using the Parkes/Murriyang telescope. It is also potentially associated with a PWN revealed by Rapid ASKAP (Australian square kilometre Array Pathfinder) Continuum Survey (RACS). This 118 ms pulsar has a high dispersion measure (DM) of ~ 873 pc cm-3 and a rotation measure (RM) of ~ -1015 rad m-2. Because of such a high DM, at frequencies below 2 GHz, the pulse profile is significantly scattered, making it effectively undetected in previous pulsar surveys at 1.4 GHz. Subsequent Parkes observations yield a period derivative of P-dot = 5.56 × 10-14 s s-1, implying a characteristics age, τc ≈ 33,800 yrs, and spin down luminosity, E-dot = 1.3 × 1036 erg s-1, placing PSR J1631-4721 in the population of energetic and rotation- powered Galactic pulsars. Our results highlights the potential to detect previously missed highly scattered pulsars through ongoing and future all-sky radio continuum surveys.
[P124] “A novel analysis of contamination in Lyman break galaxy samples based on spatial cross-correlation with intermediate-redshift galaxies” – Miftahul Hilmi
Potential contamination from low/intermediate-redshift galaxies, such as objects with a prominent Balmer break, affects the photometric selection of high-redshift galaxies through identification of a Lyman break. Traditionally, contamination is estimated from spectroscopic follow-up and/or simulations. Here, we introduce a novel approach to estimating contamination for Lyman-break galaxy (LBG) samples based on measuring spatial correlation with the parent population of lower redshift interlopers. We propose two conceptual approaches applicable to different survey strategies: a single large contiguous field and a survey consisting of multiple independent lines of sight. For a large single field, we compute the cross-correlation function between galaxies at redshiftz~ 6 and intermediate-redshift galaxies atz~ 1.3. We apply the method to the CANDELS GOODS-S and XDF surveys and compare the measurement with simulated mock observations, finding that the contamination level in both cases is not measurable and lies below 5.5% (at 90% confidence). For random-pointing multiple field surveys, we measure instead the number count correlation between high-redshift galaxies and interlopers, as a two-point correlation analysis is not generally feasible. We show an application to the LBG samples atz~ 8 and the possible interloper population atz~ 2 in the Brightest of Reionizing Galaxies (BoRG) survey. By comparing the Pearson correlation coefficient with the result from Monte Carlo simulations, we estimate a contamination fraction of 62+13-39%, consistent with previous literature. These results validate the proposed approach and demonstrate its utility as an independent check of contamination in photometrically selected samples of high-redshift galaxies.
[P013] “Investigating the Dark Matter Halos of Galaxies through Galaxy-Galaxy Lensing” – Vanshika Kansal
Weak lensing is a crucial tool in modern cosmology, pivotal to missions like Euclid, Roman, and LSST. However, conventional weak lensing (CWL) measurements are approaching a fundamental ‘shape noise limit’, arising from the random shapes/orientations of unrelated galaxies (e.g., Refregier et al. 2012; Niemi et al. 2015). To address these challenges, we pioneer precision weak lensing (PWL) methods to surpass the shape noise limit. Building upon the concepts initially proposed by Blain (2002) and Morales (2006), Gurri et al. 2020 & 2021 have demonstrated a comprehensive experimental design using Integral Field Spectroscopy observations of the lensed galaxy for PWL. This approach is particularly adept at assessing dark halo concentrations through investigations of galaxy-galaxy weak lensing at small (10-100 kpc) scales, exclusively feasible at low redshift. In these scenarios, CWL encounters challenges in attaining adequate SNR, even with missions like Euclid or Roman, as exemplified by Xu et al. (2023). My work extends Precision Weak Lensing (PWL) techniques and analysis in two complementary directions: 1.) Utilizing DEIMOS long-slit spectroscopy of background galaxies to map the shear field, enabling the determination of the mass distribution for the lens. 2.) Employing new observations of the lens galaxies to derive detailed dynamical models that provide predictions for the shear field. These predictions are then compared to independently obtained PWL measurements. My talk will unveil early findings from these approaches, illuminating progress in understanding cosmic structures through innovative PWL approaches.
[P171] “The circular velocity and Halo mass functions: Constraining baryonic Physics in the nearby Universe” – Andrei Ristea
Integral-field Spectroscopy has opened the doorway for the joint study of stellar and gas resolved motions, which has led to constraints of several galaxy statistical properties in the nearby Universe. One such metric is the circular velocity function (CVF), a fundamental prediction of the ΛCDM framework. Current observational computations of the CVF are however scarce and suffer from either very low number statistics or from a complete bias towards gas-rich objects detectable by HI surveys.
We computed the CVF in the nearby Universe by combining stellar and gas kinematics from the MaNGA galaxy Survey. This CVF rendition features a sample of galaxies with high completeness, representative of all morphological types and star-forming classes, greatly improving on previous studies in terms of sample diversity. I will discuss how different morphologies, kinematic and star-forming classes contribute to the galaxy number density in the nearby Universe at different velocities.
Leveraging the fact that circular velocities are tracing the virial equilibrium of dark matter halos, I computed the halo mass function, covering one order of magnitude in halo mass which was previously unprobed. Combining my HMF data with previous computations based on HI kinematics and group halo detections, I constrained the HMF over an unprecedented five orders of magnitude, “resolving” 73 per cent of the matter density in the nearby Universe. This empirical HMF agrees well with ΛCDM predictions.
[P172] “Meet the 49ers: A serendipitous discovery of HI-rich galaxy groups with MeerKAT” – Marcin Glowacki
Galaxy groups occupy up to 50% of the local Universe and are important parts of the hierarchical structure of the Universe. I report on the serendipitous discovery of 49 HI-rich galaxies in a short Open Time observation with MeerKAT, which make up multiple galaxy groups that were previously unknown. I present their properties such as their HI and stellar masses, and examples of galaxy interactions in the sample, as well as a potential OH megamaser. Results from preliminary findings from deeper follow-up with MeerKAT will also be presented. This finding highlights the capability of MeerKAT for other serendipitous discoveries in a remarkably short amount of observing time of other HI-rich galaxies, and the potential for many more such findings on existing Open Time datasets.
[P062] “A comparison between Shapefit compression and Full-Modelling method for DESI and beyond” – Yanxian Lai
Large-scale structures of the universe encoded in the positions of the galaxies contain valuable information on cosmic growth, which can be used to constrain cosmological parameters. Dark Energy Spectroscopic Instrument (DESI) will provide distance measurements to around 30 million galaxies, which is an order of magnitude larger than any previous surveys. Although the large amount of data will provide the tightest constraints of cosmological parameters with galaxy surveys to date, it also means that we need more precise validation of our method than any previous surveys, and a much longer computation time to analyze the data. In this talk, I will present an alternative approach called “Shapefit” to extracting cosmological parameters from the galaxy power spectrum. Different from the traditional “Full-modelling” approach, which calculates new power spectra based on input cosmological parameters at each iteration, “Shapefit” calculates the new power spectra by adjusting the template power spectrum based on four compressed parameters. The constraints of the compressed parameters can then be converted to the constraints of the cosmological parameters based on the selected cosmological model. We validated the “Shapefit” pipeline with the DESI cubic mocks, which have the same volume as the projected DESI Year-5 data without the window function. We found that “Shapefit” obtained cosmological constraints much faster than the traditional “Full-Modelling” approach. Furthermore, the constraints of cosmological parameters from “Shapefit” in the LCDM models are consistent with the “Full-Modelling” approach to within 0.3σ. Lastly, we also found similar consistency with the wCDM and oCDM models.
[P106] “LSST: Community Update” – Rachel Webster
The Legacy Survey of Space and Time, orLSST [https://rubinobservatory.org/explore/lsst] is expected to commence science operations in 2025. This talk will provide details of the current activities of the Australian LSST collaboration, and potential ways for members of the community to engage in early Science in preparation for the deluge of data expected once observations commence.
[P133] “You don’t need to download all the data! The Data Central (R)evolution” – Simon O’Toole
The long-sought-after idea of bringing the “code to the data” is now a reality. Science platforms like Data Central exist to assist astronomers to reduce, analyse and publish data. While Data Central has long been known for hosting science quality data products, we have also made great leaps in remote data reduction with 2dFdr and ESO pipelines, and will soon provide an environment for users to run reductions, analyses and even ML/AI routines on data hosted locally or available on the Virtual Observatory. This talk will cover some of the exciting new capabilities on offer and take a sneak peek at our exciting new web portal.
[P153] “The Rapid ASKAP Continuum Survey” – Stefan Duchesne
The Australian SKA Pathfinder (ASKAP) is completing a series of radio-frequency surveys as part of the Rapid ASKAP Continuum Survey (RACS). RACS covers three radio-frequency bands centred on 888, 1367, and 1655 MHz and covers the whole sky and up to declination ~+49 degrees. RACS provides a combination of frequency, sensitivity (~ 150-300 micro Jy/beam), and resolution (~8-15 arcsec) that fills a niche in the ecosystem of all-sky surveys. Various imaging and catalogue releases have been completed and are underway and focus on the Stokes I and V continuum emission of the sky accessible to ASKAP, featuring 2-3M radio sources in each of the three bands. As well as this continuum component, spectro-polarimetric work in Stokes Q and U is also underway. This update on the RACS project is on behalf of the team behind the surveys and will highlight the current and upcoming releases and general progress of RACS.
[P147] “The Future of Meetings: Current activities and opportunities for engagement” – Vanessa Moss
“The Future of Meetings” (TFOM) has existed since early 2020, initially focused on delivering the CSIRO TFOM symposium but continuing afterwards as a community of practice with an origin in and close links to Australian astronomy.
Vision
Our vision is a world that is increasingly accessible, inclusive and sustainable thanks to the benefits of advancing technology, both for the scientific community specifically and in wider society. We advocate that this vision can be realised by adapting approaches to how we meet, interact and collaborate, in order to prioritise better, more open ways of communicating.
Mission
Our mission is to build a community around the common purpose of making meetings and collaboration of all kinds more accessible and sustainable. We identify and pioneer new approaches to virtual interaction, and champion their integration into appropriate contexts. Our mission and vision are achievable by designing, exploring, evaluating and communicating ways of ensuring positive, productive and inclusive online and hybrid experiences.
TFOM x ASA
The TFOM community of practice, driven especially by active members within the Australian and Asia-Pacific context, is a global distributed collective of contributors. Our current activities include providing advice on online/hybrid design of events and meetings, experimenting with application of new technologies (especially VR and XR), direct involvement in or execution of relevant events and communication via various mechanisms on best practice for online/hybrid, among others. If you are interested and would like to learn more (or actively participate in TFOM), we’re very keen to hear from you!
[P170] “HI, FRB, what’s your z: Using radio observations to measure FRB redshifts and probe their gas environments” – Marcin Glowacki
While analysis of localised FRB host galaxies typically focuses on the stellar component, neutral hydrogen (HI), traced through the 21-cm transition with radio telescopes, informs us on the gas content of galaxies. The HI distribution can reveal to us the history of the galaxy, such as merger events that may not be evident from the stellar information alone. This is an important consideration for understanding the environments of FRBs and their progenitors. We report on HI follow-up of FRBs identified by the CRAFT survey team, including the first commensal detection and localisation of FRB 20211127I, and the detection of HI emission in the FRB host galaxy. We also report the first redshift measurement for an FRB host galaxy through radio observations of the HI content, rather than through optical spectroscopy. Other HI follow-up observations of FRB hosts with the MeerKAT and GMRT instruments will be presented, including a confirmation that the gas environment of FRB 20211127I is remarkably normal – unlike any previous detection of HI emission in an FRB host, complicating the previous picture supporting a ‘fast channel’ model for FRB progenitors.
[P094] “Early insight into operating the world’s largest radio telescope: views from the SKA-Low Telescope Operators” – Jimi Green
The Square Kilometre Array Observatory (SKAO), due to be the world’s largest radio telescope, has commenced construction. The SKAO Science Operations Team is focused on developing the operational procedures to ensure that the two telescopes that make up the observatory, SKA-Low in Australia and SKA-Mid in South Africa, will be ready to deliver transformational science. In this presentation, we will give an insight to the interfaces and tools used to operate the preliminary Aperture Array Verification System (AAVS3), together with the planned interfaces and tools to operate the first stage of the telescope rollout, Array Assembly release 0.5, ‘AA0.5’, due to be operational in the coming months. We will note opportunities to contribute thoughts, experiences and lessons learnt.
[P045] “Discovery of a stellar merger population: Carbon-deficient red giants” – Simon Campbell
Carbon-deficient red giants (CDGs) are a peculiar class of stars that have eluded explanation for decades. We use asteroseismology combined with spectroscopy and astrometry to better characterise the CDGs, discovering 15 new CDGs in the Kepler field. Remarkably, we find that our CDGs are almost exclusively in the red clump (RC) phase. Asteroseismic masses reveal that our CDGs are primarily low-mass stars (M <= 2 Msun), in contrast to previous studies, which suggested they are of intermediate mass based on HR diagrams. Surprisingly, a very high fraction of our CDGs are also Li-rich giants (50%). We find a bimodal distribution of luminosity in the CDGs, with one group having normal RC luminosity and the other being a factor of 2 more luminous than expected for their masses. Based on demarcations in chemical patterns and luminosities, we discuss various formation scenarios in light of our new dataset and conclude that a merger of a helium white dwarf with a red giant branch star is the most likely scenario for the overluminous stars. Due to the overlap with the CDGs, Li-rich giants may have similar formation channels.
[P177] “A search for fast outflows of cold gas through HI absorption” – Marcin Glowacki
It is well established that AGN feedback plays a crucial role in the evolution of galaxies, but observational evidence of the physical properties of these feedback processes remains elusive. One such signature of feedback are fast outflows of cold gas observed in a number of powerful radio galaxies. The sensitivity of the MeerKAT radio telescope, combined with the wide frequency coverage on a radio-quiet site, means it is uniquely suited for searching for these outflows at intermediate redshifts where feedback processes are playing a critical role in quenching star-formation and transforming galaxies. We present results of a search for these fast cold gas outflows with MeerKAT, targetting neutral hydrogen (HI) absorption detections from the FLASH survey on ASKAP. We also present new HI absorption detections made by MeerKAT toward other radio-bright sources within the field of view of our targetted observations. These observations help to shed light on how galaxies have evolved over the past 8 billion years and provide a much needed observational basis to inform future simulations of galaxy evolution.
[P165] “On the accuracy of dark matter halo merger trees & consequences for semi-analytical models of galaxy formation” – Angel Chandro Gomez
Semi-analytic models (SAMs) are a powerful tool for making theoretical predictions for galaxies across cosmic time. They follow the growth of galaxies based on the halo assembly histories from large N-body cosmological simulations, requiring the use of codes that find (halo finder) and track the time evolution (tree builder) of these halos. However, it has been widely reported in the literature that these codes give rise to numerical issues when dealing with merging massive systems. In this talk we present how relevant these issues are on state-of-the-art cosmological boxes and study how they impact the galaxy predictions coming from the SAMs. We characterize 2 major numerical artifacts (nonphysical events in which halos swap huge amounts of mass and massive halos that show up unexpectedly) in the halo assembly histories of the FLAMINGO and PMillennium simulations, with the novelty of quantifying them in detail. More than 50% of the more massive halos at z=0 inherit them, with numbers above 90% for the most massive bins. At the same time, running the SAM SHARK we discover peaks in the star formation for the galaxies hosted by nonphysical halos whenever the numerical artifact is happening. Our main conclusion is that these numerical issues arise independently of the halo finder and tree builder codes, and they must be accounted for when running semi-analytical galaxy formation models. Our work will have implications for the modelling of massive galaxies across cosmic time.
[P195] “Outflows in the Planetary Nebula NGC 6445 I: Morphology and kinematics” – Hecsari Bello Martinez
A morpho-kinematic study of the planetary nebula (PN) NGC 6545, utilizing direct imaging and high-resolution spectra focused on the H and NII emission lines, was performed for comprehending the evolution of this object. The reduction and calibration processing of the PN spectra was made using the IRAF software and the FrameGoTools routine. Additionally, by means of a Python routine, the unsharp-masking technique was applied on the Position-Velocity (PV) diagrams, in order to highlight the PN structures. A morpho-kinematic model is obtained through the Shape software and the PVs diagrams. In this model, the absence of a central ring is verified, as well as the presence of a pair of main lobes and two additional internal structures.
Some of these lobes have been previously reported by different authors in NII, SII and H observations. It is believed that the absence of a central ring in NGC 6545, the break-up of several structures and the filamentary part, is due to the evolved central star, the discontinuity of the outflow density and the violent interaction of the ejected wind when forming the lobes.
[P156] “PeVatrons: The Most Extreme Particle Accelerators in our Galaxy” – Sabrina Einecke
Cosmic rays play a crucial role in the evolution of galaxies, but their origin poses one of the biggest mysteries today. Their spectrum suggests the existence of so-called PeVatrons – astrophysical objects that accelerate particles up to at least PeV energies. However, we cannot trace them back to their accelerator, as they are deflected by interstellar magnetic fields. To hunt these extreme accelerators in our Galaxy, we therefore need to use alternative messengers such as gamma rays or neutrinos, which are produced in interactions involving cosmic rays. With the recent commissioning of the ultra-high-energy gamma-ray observatory LHAASO, we got a first glimpse of were these PeVatrons are located in our Galaxy. The next – much more crucial – milestones are to identify the astrophysical objects behind them and reveal the particles that are accelerated (i.e. hadrons or leptons).
This contribution will highlight key results on the search for Galactic PeVatrons and review strategies to achieve the milestones, encompassing data from the next-generation gamma-ray observatory CTAO and Australian radio surveys, among others.
[P140] “A Rare Periodic Nuclear Transient – ASASSN-14ko” – Jennifer Shi
Supermassive Black Holes at the heart of nearby galaxies can exhibit themselves as Active Galactic Nuclei (AGNs). AGNs are usually modeled as a damped random walk since they change stochastically over all wavelengths on the electromagnetic spectrum. However, observations of evenly spaced AGN flares may indicate the existence of a binary supermassive black hole system. Since periodic AGN flares are extremely rare it gives us a unique opportunity to peer into the accretion process of SMBHs in real time which is why the discovery of ASASSN-14ko is exciting.
ASASSN-14ko exhibits periodic, multiwavelength flare emission every 115 days. The exact cause of ASASSN-14ko’s periodic flares is still unknown with currently favoured theory suggests that it is the result of a partial TDE that occurs from stellar material of a giant star being stripped away during each pericenter passage or from a SMBH binary.Using the Wifes 2.3m telescope, the recent three flares have been spectrally monitored with near daily cadence.
[P191] “The tale of two streams separated by an ocean” – Adithya Balasubramaniam
Stellar streams – formed through the tidal disruptions of dwarf galaxies and star clusters –can tell us about the nature of their progenitors as well as the distribution of mass inside their orbits. The Southern Stream Stellar Spectroscopic Survey (S5) employs the Anglo-Australian Telescope (AAT) to study stellar streams, using photometric and proper-motion data to identify candidate member stars and AAOmega spectra to obtain radial velocities and abundance information. Work done by S5 has explored stream membership, orbit models and progenitors in detail. S5 also takes high resolution follow-up spectra for confirmed stream members to analyze their detailed properties and better understand the evolutionary histories of progenitor dwarf galaxies and globular clusters. I will present an in-depth study and comparison of two metal-poor, distant stellar streams originally identified in the Dark Energy Survey: Elqui and Turranburra – the latter named after Sydney’s Lane Cove River. Both dwarf galaxy streams are rather distant, with Elqui at a Galactocentric distance of 52 kpc and Turranburra at 26 kpc. In previous work, both streams have been found to have high velocity dispersions and low mean metallicities, implying that their progenitors were relatively low-mass dwarf galaxies.Through studying the dynamics and properties of these two streams, we are increasing our understanding of the accretion history of the Milky Way, as well shedding light on the broader processes that shape galaxy formation in general.
[P026] “A step toward SKA-Low: The Aperture Array Verification System 3 (AAVS3)” – Danny Price
The Square Kilometre Array (SKA) telescope will be one of the most sensitive instruments ever built. In March 2024, the first antenna of more than 130,000 antennas that will make up the SKA’s low-frequency aperture array, SKA-Low, was installed on Wajarri Country in the Mid West of Western Australia. However, work to verify the SKA-Low design began well before this symbolic milestone: a series of prototype stations known as the Aperture Array Verification Systems, or AAVS, informed the final design of SKA-Low. In this talk, I will give an overview of recent science commissioning work performed on the AAVS3 technology demonstrator, deployed at Illyarimanha Ilgari Bundara, the CSIRO Murchison Radio-astronomy Observatory. AAVS3 operates over 50-350 MHz, and consists of 256 two-metre tall ‘SKALA’ antennas — as will be used in SKA-Low — arranged within a 38-m diameter area.
[P197] “Dust formation in common envelope binary interactions.” – Luis Bermudez
We conducted numerical simulations of a common envelope (CE) interaction between 1.7 M⊙ and 3.7 M⊙ thermally-pulsing asymptotic giant branch (AGB) stars, with their 0.6 M⊙ compact companion. We use tabulated equations of state to take into account recombination energy. For the first time, formation and growth of dust in the envelope is calculated explicitly, using a carbon dust nucleation network with a C/O abundance ratio of 2.5. The total dust yield was about 8.2 × 10−3 M⊙ and 2.2 × 10−2 M⊙ for the 1.7 M⊙ and 3.7 M⊙ AGB stars, respectively, with a nucleation efficiency near 100% when dust destruction is absent. Dust primarily formed in unbound material, minimally impacting mass ejection and orbital evolution. Dust grains initially emerge within approximately 1-3 years after the onset of the CE, swiftly constructing an optically thick shell at around 10-20 au. This shell then increases in both thickness and radius, reaching values of about 400 to 500 au within approximately 40 years. These sizable objects maintain temperatures near 400 K. Despite dust yields being comparable to those of single AGB stars of similar mass, the formation of dust within CE ejections occurs over decades rather than tens of thousands of years. This swift dust creation could potentially explain the shift in the infrared spectral energy distribution observed in some optical transients, such as luminous red novae. Our simulations also suggest a link between dusty CEs and extreme carbon stars, supporting the idea of “water fountains” being post-CE objects.
[P111] “RadioGalaxyNET: Dataset and Novel Computer Vision Algorithms for the Detection of Extended Radio Galaxies and Infrared Hosts” – Nikhel Gupta
Creating radio galaxy catalogues from next-generation deep surveys requires automated identification of associated components of extended sources and their corresponding infrared hosts. In this talk, I’ll present RadioGalaxyNET, a multimodal dataset, and a suite of novel computer vision algorithms designed to automate the detection and localization of multi-component extended radio galaxies and their corresponding infrared hosts. The dataset comprises 4,155 instances of galaxies in 2,800 images with both radio and infrared channels. Each instance provides information about the extended radio galaxy class, its corresponding bounding box encompassing all components, the pixel-level segmentation mask, and the keypoint position of its corresponding infrared host galaxy. RadioGalaxyNET is the first dataset to include images from the highly sensitive Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope, corresponding infrared images, and instance-level annotations for galaxy detection. We benchmark several object detection algorithms on the dataset and propose a novel multimodal approach to simultaneously detect radio galaxies and the positions of infrared hosts.
[P073] “Clustering and physical properties of the star-forming galaxies and AGN: does assembly bias have a role in AGN activity?” – Amrita Banerjee
We compare the spatial clustering and physical properties of the active galactic nuclei (AGN) and star-forming galaxies (SFG) at fixed stellar mass using a volume limited sample from the SDSS. The AGN prefer the denser regions and are strongly clustered than the SFG at smaller scales. We compare the distributions of the colour, star formation rate (SFR), D4000 and morphology of the AGN and SFG after matching their stellar mass distributions. The null hypothesis can be rejected at > 99.99% confidence level in each case. The comparisons are also carried out at different densities. The differences persist at the same significance level in both the low and high density regions, implying that such differences do not originate from the variations in the density. An analysis of the correlations between the different physical properties at fixed stellar mass reveals that the anticorrelations of SFR with morphology, colour and recent star formation history are 2-3 times stronger for the AGN than for the SFG. It suggests that the presence of a bulge and the availability of gas are the most crucial requirements for AGN activity. We propose a picture where the galaxies at fixed stellar mass may have widely different assembly histories, leading to significant variations in bulge properties and cold gas content. The development of the suitable conditions for AGN activity in a galaxy remains uncertain due to a broad diversity of assembly history. We conclude that the AGN are stochastic phenomena owing to an underlying role of the assembly bias.
[P007] “Stellar Tango: Exploring the Cosmic Dance of Counter-Rotating Galactic Disks in GECKOS” – Jesse van de Sande
In 1983, astronomers using Australian telescopes discovered an ancient “thick disk” of stars in the Milky Way. This faint, thick disk defies easy explanation but may hold the key to understanding disk formation. Four decades later, we now know that the Galactic thick disk is distinct from the dominant thin disk through its unique stellar chemistry and age. However, there is no consensus on how the thin and thick disks formed and evolved, and the answer is unlikely to come from studying our Milky Way alone. In GECKOS, a new VLT/MUSE large program studying edge-on galaxies, we have discovered a galaxy with a counter-rotating thick disk that may provide insight into the long-standing question of the merger origin of the thick and thin disks. In this talk, I will present stellar kinematic and stellar population measurements of this galaxy to construct a comprehensive picture of its assembly history. This work will underscore the potential of the immense discovery space that the GECKOS survey offers.
[P183] “The spatially resolved relation between dust-to-gas and metallicity with TYPHOON survey” – Hye-Jin Park
The relation between the dust-to-gas mass ratio (DGR) and gas-phase metallicity (Zgas) (i.e., DGR-Zgas relation) is an important tool for measuring the gas content of high-z galaxies. However, the form of DGR-Zgas relation is still uncertain especially in the low-metallicity regime most applicable to the early universe. With recent large integral field spectroscopic (IFS) surveys of very nearby galaxies, we now have spatially resolved observations of dust, gas, and metal abundances to gain new perspective on the local variance of DGR in galaxies. In this talk, I will present the spatially resolved DGR-Zgas relation in 11 local galaxies using the large field-of-view (≳ 3′) optical pseudo-IFS data taken by the TYPHOON/PrISM survey and multi-wavelength data (far-UV to far-IR, CO, and HI 21 cm radio). The spatially resolved DGR-Zgas relation shows a shallower decrease in DGR toward low-metallicity systems relative to previous globally-based estimates. In addition, for a better understanding of the cycle of interstellar medium in low-metallicity systems, I will show the spatially resolved relation between dust, metallicity, and cold HI gas, whose information is found via profile decomposition method using spatial coherency with neighboring regions.
[P113] “Deriving Stellar Parameters and abundances: Employing “The Cannon” to Bridge GALAH-DR4 to GAIA-RVS Spectra” – Pradosh Barun Das
The enormous spectroscopic datasets from current astronomical surveys provide an unprecedented opportunity to explore the stellar populations of the Milky Way and its surroundings. The largest surveys range from several million stars (e.g., LAMOST) to the roughly quarter-billion stars observed with Gaia XP spectra. These survey data are generally at low or moderate spectroscopic resolutions, yet the “gold standard” for determining stellar parameters and elemental abundances remains high-resolution spectroscopic data. We have usedThe Cannon, a largely Australian-developed, data-driven method to transfer labels from high-resolution reference data to lower-resolution data, specifically applying stellar parameters and abundances derived from GALAH data (GALAH iDR4) to Gaia RVS spectra (Gaia DR3). We trained our data model on ~14000 selected targets common to both the surveys, utilising the stellar labels from GALAH. With this model, we are able to consistently predict stellar parameters such as Teff, log g, [Fe/H], and abundances of several alpha elements for over 800,000 Gaia RVS spectra. Using stars from several open and globular clusters present in the Gaia RVS catalogue, we have validated our metallicity estimates. Finally, for a subset of this sample with predicted log g < 3.5 (i.e., giants) we are able to measure the abundances of several neutron-capture elements, illustrating the exciting potential of this method for reliably determining stellar parameters and abundances from medium-resolution Gaia RVS spectra – a dataset which, by the end of the Gaia mission, is expected to include over 30 million stars.
[P042] “Radio detected galaxies are more obscured than optically selected galaxies” – Tania Ahmed
We demonstrate the importance of radio selection in probing heavily obscured galaxy populations. We combine Evolutionary Map of the Universe (EMU) Early Science data in the Galaxy and Mass Assembly (GAMA) G23 field with the GAMA data, providing optical photometry and spectral line measurements, together with Wide-field Infrared Survey Explorer (WISE) infrared (IR) photometry, providing IR luminosities and colours. We investigate the degree of obscuration in star forming galaxies, based on the Balmer decrement (BD), and explore how this trend varies, over a redshift range of 0 to 0.345. We demonstrate that the radio detected population has on average higher levels of obscuration than the parent optical sample, arising through missing the lowest BD and lowest mass galaxies, which are also the lower star formation rate (SFR) and metallicity systems. We discuss possible explanations for this result, including speculation around whether it might arise from steeper stellar initial mass functions in low mass, low SFR galaxies.
[P027] “Complex Radio to Infrared SED modelling of nearby Star Forming Galaxies” – Joe Grundy
Recent work modelling the broadband radio to infrared spectral energy distributions (SEDs) of star-forming galaxies (SFGs) by Clemens et al. (2010), Galvin et al. (2018) and Dey et al. (2022, 2024) have found a population of (ultra) luminous infrared galaxies that exhibit spectral curvature at low frequencies (ν ≤ 300 MHz). This curvature is thought to be caused by free-free absorption (FFA) as star-forming regions become optically thick to radio emission.
We extend this analysis to a lower luminosity handcrafted sample of nearby GLEAM (70-230MHz) detected SFGs including 12 with low frequency turnovers (LFTOs) and 8 control sources and observed them with ATCA and ALMA. During our initial SED modelling we find that most SFGs have most preferred models which include FFA or synchrotron losses rather than simple one or two component power-laws. We however find limited evidence for global properties which are responsible for causing these SED features indicating they are likely caused in specific galactic regions which are usually integrated over a synthesised beam.
We performed a resolved analysis of the radio and infrared emission of these SFGs to create star formation surface density, spectral index and infrared-radio correlation maps as well as ALMA CO molecular gas maps to see whether we can identify the regions responsible for increased SED complexity.
This work will be important in the SKA era as large numbers of SFGs will be detected and understanding the physical mechanisms within SFGs that result in increased SED complexity will be key to interpreting SKA data.
[P012] “RG-CAT: Detection Pipeline and Catalogue of Radio Galaxies in the EMU Pilot Survey” – Nikhel Gupta
In this talk, I will present source detection and catalogue construction pipelines to build the first catalogue of radio galaxies from the 270 deg2 pilot survey of the Evolutionary Map of the Universe (EMU-PS) conducted with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope. The detection pipeline uses Gal-DINO computer-vision networks to predict the categories of radio morphology and bounding boxes for radio sources, as well as their potential infrared host positions. The Gal-DINO network is trained and evaluated on approximately 5,000 visually inspected radio galaxies and their infrared hosts, encompassing both compact and extended radio morphologies. The Intersection over Union (IoU) for the predicted and ground truth bounding boxes is larger than 0.5 for 99% of the radio sources, and 98% of predicted host positions are within 3′′ of the ground truth infrared host in the evaluation set. The catalogue construction pipeline uses the predictions of the trained network on the radio and infrared image cutouts based on the catalogue of radio components identified using the Selavy source finder algorithm. This results in identifications for a total of 211,625 radio sources, with 201,211 classified as compact or unresolved. The remaining 10,414 are categorized as extended radio morphologies, including 582 FR-I, 5,602 FR-II, 1,494 FR-x (uncertain whether FR-I or FR-II), 2,375 R (single-peak resolved) radio galaxies, and 361 with peculiar and other rare morphologies. Cross-matching the radio sources with infrared and optical catalogues yields infrared counterparts for 73% and photometric redshifts for 36% of them.
[P185] “Sub-arcsecond scale sources identified with ASKAP and the MWA: studying population changes and enabling space weather studies” – Rajan Chhetri
Active Galactic Nuclei at radio frequencies span a wide range in angular sizes. Understanding the low frequency population at sub-arcsecond scale is important to understand the evolution of radio galaxies. However, identifying them in large numbers has been difficult at frequencies below 1 GHz. With the new generation of radio telescopes operating at low frequencies, overcoming this challenge will allow us to better understand the evolution of radio galaxies.
We have developed the technique of widefield interplanetary scintillation (IPS) with the Murchison Widefield Array (MWA). IPS is the radio analogue of the twinkling of stars at night, but induced by the solar wind. This technique very efficiently identifies sub-arcsecond scale compact objects in large numbers (~300 objects are identified with compact structure from ~900 sq. deg. with only 10 minutes of observation). We are currently extending this technique to use the wide field of view of the ASKAP radio telescope, identifying ~130 sub-arcsecond scale objects with just 2.5 minutes of observation at 888 MHz.
The identification with the MWA showed us that the compact source population at low frequencies is quite different from its gigahertz counterpart. The blazar population, which is dominant at gigahertz frequencies, gives way to peaked spectrum sources as the dominant population at low frequencies. I will demonstrate these changes in the population of compact sources as a function of frequency using both the MWA and the recent ASKAP results. Then, I will outline how compact sources from MWA and ASKAP enable space weather studies.
[P121] “Young radio AGN: from first identification to population-scale studies” – Emily Kerrison
Identifying the very youngest radio AGN, in which the jets have yet to break out through the ISM of their host, is key to understanding their formation, duty cycle, and co-evolution. We know these radio sources exhibit a peak in their spectral energy distribution (SED), but this peak can be a challenge to detect owing to the number of flux density measurements required. I shall discuss here an application of RadioSED, a new Bayesian SED fitting tool, to identify these young AGN within the Stripe 82 field. I will show how we can, for the first time, capture spectral peaks from megahertz through to tens of gigahertz in a uniform way, which allows us to not only recover all 11 previously published young radio AGN, but to increase this sample by over an order of magnitude, bringing their total to well over 100 in a modest 300deg2of sky. I shall then discuss how we can use broadband radio spectra in conjunction with mutliwavelength data spanning radio to X-ray wavelengths to better understand the multi-phase gas in these most compact radio AGN, with a particular focus on radio spectral data from the First Large Absorption Survey in HI (FLASH), and X-ray data from the eROSITA all sky survey (eRASS). I end by placing this in the context of new and forthcoming untargeted surveys of the SKA era, which offer us an unprecedented opportunity to explore the interaction between young radio sources and the ISM of their host galaxies.
[P071] “First result from the CRAFT COherent upgrade (CRACO): Exploring transient radio sky on millisecond to second timescales” – Ziteng Wang
Short-duration radio transients are often associated with energetic events in the Universe. The discovery of more such transients will help us understand the critical information for these events, such as the progenitors and the key physical parameters of the event. In this talk, I will present the first results made using a new backend on the Australian Square Kilometre Array Pathfinder, CRAFT Coherent upgrade (CRACO), which enables us to record the correlated visibilities with tens of millisecond time resolution. This upgrade is helping us probe an hitherto unexplored part of the transient parameter space with a large field-of-view survey imaging telescope like ASKAP. We have so far discovered 15 new fast radio bursts (FRBs), 8 new pulsars/rotating radio transients, and 2 new ultra-long period transients (with a period of 44 mins and 6.5 hours respectively) in the first 2000 hours of our pilot survey. Out of these, notably, we’ve found that one source is a repeating FRB, one is a highly scattered FRB, and one is a slow-rotating pulsar (40 s). The discovery of these sources hints at the existence of a larger population of sources that was not previously known to exist. I will also discuss the future plan for CRACO including real-time detection and higher time-resolution data searching.
[P098] “ASKAP J1839-0756 – a ULPO candidate with a period of 6.45 hours” – Yu Wing Joshua Lee
Ultra-long period objects (ULPOs) represent a unique class of radio transient objects, with only a few having been identified to date. These objects emit highly polarised, coherent pulses with widths of tens of seconds to several minutes and periods ranging from a few tens of minutes to approximately an hour. Their location in the radio transient phase space clusters in an as-yet unexplored region near the boundary between coherent and incoherent sources, offering a possible connection between the emission mechanisms of both types. We present here the discovery of ASKAP J1839-0756 which emits ~90% linearly polarised radio pulses lasting ~1400 seconds every 6.45 hours. This makes it a ULPO candidate with the longest period recorded to date. The radio emission properties suggest a compact object origin, which can be a neutron star or a white dwarf that is either isolated or in a binary system. The spiky, short timescale sub-structure in the pulse is reminiscent of magnetars, while the steep spectral index of -2.7 is similar to the mysterious Galactic Centre Radio Transient. In this presentation, I will introduce recent observational results and possible progenitor models of this source, and discuss its position in the emerging ULPO population.
[P188] “Dynamics of young star-inner disk interaction (and impact of embedded planets): an observational perspective” – Laura Venuti
Technological advances over the last decades have allowed us to achieve an unprecedented view of protoplanetary disks around young stars. In particular, dedicated surveys of star-forming regions with Kepler/K2 have documented a large variety of time domain behaviours that can be found among young star-disk systems. These behaviours, ranging from ordered modulated patterns to stochastic and bursting patterns, reflect varying physical conditions within the inner disk and a gradient in mass accretion dynamics onto the star. For a select class of young stellar variables, known as dippers, favourable viewing geometries grazing the disk plane provide a direct window onto the structure of the inner disk regions and of the accretion streams that form there. At the same time, the isotropic outer disk inclinations that have been measured for dipper stars in ALMA surveys suggest that inner/outer disk misalignments may develop frequently during the protoplanetary disk phase, possibly tracing perturbations by a stellar companion or a planetary-mass object. During this talk, I will review these recent results and explore what these observations teach us regarding the dynamical evolution of young stars and their disks.
[P186] “First Results from the ALMA Planet Hunting Campaign — The exoALMA Large Program” – Christophe Pinte
Exoplanetary systems show an incredible diversity, hosting planets with a vast range of masses, radii, and orbital separations. However, it is unclear whether this diversity stems from a distribution of initial conditions, and/or the result of multiple planet formation pathways. It is therefore fundamental to detect young, embedded planets during the process of formation. While the planets likely remain hidden by the disk at near-infrared wavelengths, they leave clear signatures in the velocity field in their vicinity, which can be detected with line observations with ALMA. This led to the developement of the “disk kinematic” planet detection method in the last 5 years, and offers a unique opportunity to probe the distribution of planets at the extreme earliest stages of their formation.
In this contribution, we present the results of the exoALMA planet-hunting campaign that targeted 15 protoplanetary disks with deep, high spatial, and high spectral resolution observations line observations. We will discuss our planet detection statistics, the constraints we can place on these youngest planets, and their implication for the planet formation pathways, as well as our new kinematic view of the physical processes at play during planet formation.
[P181] “Fool’s Gold in the hunt for Galactic stellar mass black holes” – Tyrone O’Doherty
Black hole hunting in the Galaxy has recently experienced a Renaissance. Until 2018, all of the confirmed Galactic black holes were initially identified via X-rays produced through accretion. However, accretion will only occur in a small fraction of Galactic binaries that contain a black hole, rendering the vast majority invisible. The emergence of large all-sky photometric, spectroscopic, and astrometric surveys is enabling exciting new ways to search for black holes hidden in detached binaries. Today, we know of 5 detached black hole systems in the Galaxy, bringing the total number of confirmed black holes in the Galaxy to 30 (of an estimated 10^8). However, the number of detached black hole claims that have been debunked far outnumbers the number of confirmed black holes. In this talk, I will discuss recent work we carried out investigating different methods of black hole identification. When using photometric modulation, contact binaries provide a strong source of contamination resulting in the sample containing too many false-positives to identify real black holes. When using radial velocities, we found that all but one of the ~20 promising candidates are unlikely to host black holes. I will then present the results of a spectroscopic and photometric follow-up we carried out of this one remaining system. While black hole hunting is possible in a way like never before, devising reliable methods of finding them has proven challenging.
[P015] “The variable evolution of accretor stars in binary systems due to accretion of increasingly helium-rich material” – Sean Richards
The recent discovery of intermediate-mass helium stars presents a shift in our understanding of interacting binaries. In particular, the creation of these binaries implies that the accretor will possess an unusual chemical gradient. In this talk I will discuss the implications for binary evolution when mass transfer is assumed to be increasingly helium-rich. I will discuss how this affects all facets of a star’s future evolution, including creating cases where layers of hydrogen sit sandwiched between a helium core and helium surface in the interior profile of the star. I will briefly touch on the implications of this helium-rich mass transfer on the observation of type Ib/c and type IIb supernovae.
[P034] “The Limiting Factor: Decoding the Extreme Atmospheric Dynamics of the Ultra-hot Jupiter KELT-9b” – Nicholas Borsato
Ultra-hot Jupiters (UHJs) are an extreme form of exoplanet with equilibrium temperatures over 2000 K and are completely inhospitable to life as we know it. KELT-9b, the hottest of this class, maintains a temperature higher than most stars (Eq ~ 4000 K). The fervid nature of UHJs rules them out as targets for habitability studies; their atmospheres are largely atomic, and their proximity to their host stars drives wind speeds to the order of tens of km/s. However, their characteristics do hold one distinct advantage: they are easier to observe and characterise than other exoplanets. Ultra-hot Jupiters, like KELT-9b, can act as laboratories for observational techniques, enabling us to hone our observational abilities, while also providing insights into planetary evolution, formation, and characterisation. Our research focuses on characterising the atmospheric dynamics of KELT-9b using the cross-correlation technique. With 13 transits observed using high-resolution spectrographs across 7 observing facilities, we detected 38 atomic and ionised species in the planet’s atmosphere. We found a large diversity in the measured velocities of these detections, with considerable offsets from the true planetary velocity. We use these results, in conjunction with theoretical predictions about UHJ atmospheres, to infer that each detection occurs in different regions of the atmosphere. In effect, each species becomes a probe to map the dynamical characteristics of KELT-9b’s inflated and extensive atmosphere. Our findings demonstrate that the cross-correlation technique can probe different regions of an exoplanet’s atmosphere and decode the dynamic mechanisms at play.
[P073] “Clustering and physical properties of the star-forming galaxies and AGN: does assembly bias have a role in AGN activity?” – Amrita Banerjee
We compare the spatial clustering and physical properties of the active galactic nuclei (AGN) and star-forming galaxies (SFG) at fixed stellar mass using a volume limited sample from the SDSS. The AGN prefer the denser regions and are strongly clustered than the SFG at smaller scales. We compare the distributions of the colour, star formation rate (SFR), D4000 and morphology of the AGN and SFG after matching their stellar mass distributions. The null hypothesis can be rejected at > 99.99% confidence level in each case. The comparisons are also carried out at different densities. The differences persist at the same significance level in both the low and high density regions, implying that such differences do not originate from the variations in the density. An analysis of the correlations between the different physical properties at fixed stellar mass reveals that the anticorrelations of SFR with morphology, colour and recent star formation history are 2-3 times stronger for the AGN than for the SFG. It suggests that the presence of a bulge and the availability of gas are the most crucial requirements for AGN activity. We propose a picture where the galaxies at fixed stellar mass may have widely different assembly histories, leading to significant variations in bulge properties and cold gas content. The development of the suitable conditions for AGN activity in a galaxy remains uncertain due to a broad diversity of assembly history. We conclude that the AGN are stochastic phenomena owing to an underlying role of the assembly bias.
[P060] “The role of galaxy-scale outflows in quenching star formation” – Rebecca Davies
Outflows fundamentally alter the chemical composition, structure, and star-formation activity of galaxies, and are therefore one of the most important processes shaping galaxy evolution. However, our knowledge of the driving mechanisms, properties and impact of outflows is still in its infancy. In this talk, I will review our current understanding of how outflows contribute to star-formation quenching, with a particular focus on AGN-driven outflows during the peak epoch of star-formation and black hole growth. I will also discuss exciting new results from state-of-the-art facilities such as the James Webb Space Telescope (JWST) and the Atacama Large Millimeter Array (ALMA) which are opening the door to a new era of outflow studies at z > 4.
[P044] “Predicting the Non-Thermal Pressure in Galaxy Clusters” – Andrew Sullivan
Galaxy clusters are important astrophysical environments for understanding the interplay between dark matter halos and their hot gaseous atmospheres. Typically, the halo mass of galaxy clusters is observationally recovered from the emission of its hot, X-ray emitting gas, through the assumption of hydrostatic equilibrium. However, this equilibrium correspondence between the halo mass and the gas emission is known to be compromised in the presence of ‘non-thermal pressure’ (NTP). NTP is all the pressure that is not the gas’ thermal pressure, and is created by mergers, shocks and feedback. As the amount of NTP in the cluster’s outskirts is directly related to the ‘hydrostatic bias’ – the offset between the hydrostatic equilibrium estimate for the halo mass and the true halo mass – quantifying the NTP profile in clusters is of high importance for reliable halo mass estimates.We compare our analytic, hydrostatic equilibrium model of galaxy clusters to observational constraints on the entropy profile, and we find that without NTP, the hydrostatic equilibrium prediction systematically overestimates the entropy’s logarithmic slope by ~25%. This allows us to predict the required fraction of NTP to total pressure that must be introduced to the model. We find the NTP fraction to be an increasing function of cluster radius, reaching the value of ~20% at R500, in excellent agreement with predictions from non-radiative simulations. This NTP profile imposes a hydrostatic bias of ~12% in the halo mass M500, when measured within R500. Our results suggests that NTP contributes significantly to the hydrostatic state of galaxy clusters.
[P010] “Investigating galaxy evolution pathways through the stellar populations of bulges and disks” – Sabine Bellstedt
The processes that drive galaxy evolution, such as gas accretion, star formation, mergers, and AGN activity, have different impacts on the mass growth and quenching of galaxy bulges and disks. Using multiwavelength photometry, we apply the simultaneous spectral and spatial decomposition code ProFuse on galaxies from the GAMA survey to extract the structural bulge/disk properties of these galaxies, as well as their stellar populations. With this new technique, we identify the typical population of galaxies with ancient bulges much older than their disks, but also a smaller subset of galaxies for which this trend no longer holds. For these galaxies, not only are the bulges younger than their disks, but the disks themselves tend to be older. I will present this new analysis, and the implications for the formation and evolution mechanisms that this diversity of population properties likely points to.