The space between stars in galaxies is filled with interstellar gas. When close to hot young stars, this gas gets excited, producing emission lines that can be detected in a galaxy’s spectrum. The first step of this project involves combining a sophisticated model for the gas emission, MAPPINGS, with a model of galaxy continuum emission that is widely used by extragalactic astronomers, MAGPHYS. The result will be a complete and physically consistent characterisation of the emission by stars, ionised gas, and dust in galaxies. The second step will be a thorough investigation of the effects of different assumptions on stellar populations (for example, the effect of stellar binaries and the initial mass function) and dust on the emitted spectrum. Finally, the new code will be applied to characterize the physical properties of galaxies in existing spectroscopic surveys such as SAMI and DEVILS, and used to make predictions for surveys of distant galaxies with the upcoming James Webb Space Telescope.
The radio emission of star-forming galaxies typically contains three components: free-free emission produced by deceleration of electrons when deflected by other ions in HII regions, synchrotron emission produced by relativistic electrons trapped in spiralling orbits in strong magnetic fields, and synchrotron self-absorption. In star-forming galaxies, observations show that the radio emission correlates remarkably well with the star formation as traced by the far-infrared emission (the well-known radio/far-IR correlation), which means that the radio continuum emission could be used to measure star formation rate in radio surveys (e.g., Wallaby and EMU surveys with ASKAP). However, the physical origin of the radio/SFR correlation is still not well understood and the relation has not been calibrated enough to be applicable to any galaxy sample. The goal of this project is to use a novel, physically-motivated approach to model the radio emission of star-forming galaxies, that will be based entirely on the star formation properties. This new model will then be used to: 1) disentangle the physical drivers of the radio/SFR correlation in large samples of galaxies observed across the electromagnetic spectrum (including the radio), such as GAMA (local galaxies) and COSMOS (high-redshift), and 2) calibrate new radio-based SFR indicators specifically tailored for the upcoming ASKAP samples.
