Mr Andrew Sullivan

I am a second-year PhD student at ICRAR-UWA and I am interested in dark matter, its structure within ‘dark matter halos’, and most importantly, in understanding the relationship between the properties of these halos and astrophysical observables.  I completed a Bachelor of Philosophy Honours, with a double major in Physics and Mathematics, at the University of Western Australia here in Perth, with one of those years spent studying abroad at the University of Canterbury in Christchurch, New Zealand.

My passion is and always has been science. In particular, it excites me that there remains so much that we do not know about the world and the Universe around us. As it stands, the Universe is thought to be made from about 70% dark energy, 25% dark matter, and just 5% of ordinary matter. As we are essentially blind to 95% of our Universe, research in astrophysics is an exciting and wide-open scientific frontier, with implications as colossal as the future of our Universe and its distant past. 

So far during my PhD I have researched the mathematical relationship between the kinematic observables of dark matter halos and the halo mass (1), and the relationship between the X-ray emission observables of galaxy cluster-scale dark matter halos and the halo mass (2). Understanding this relationship between the halo mass and astrophysical observables is pivotal to informing constraints on the Halo Mass Function, which excites the prospect of constraining the fundamental properties of the dark matter particle.

Recently, I constrained the ‘non-thermal pressure’ of galaxy clusters by applying mathematical constraints to their entropy profiles in the cluster’s outer region (3). This work directly informs us about the ‘hydrostatic bias’ of galaxy clusters, or in other words, the amount in which X-ray halo mass constraints are incorrect due to the presence of non-thermal pressure.

I am currently working on an ‘inside-out’ model for jet feedback due to a galaxy cluster’s central Active Galactic Nucleus (AGN). I am interested in constraining the velocity kick that the AGN can give its gaseous atmosphere, and consequently the amount of non-thermal pressure predicted for a range of jet powers. This will allow us to link our previous constraint for the non-thermal pressure in the cluster’s outskirts to the complex feedback occurring in the cluster’s core.

Publications:

(1) https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1323358024000183

(2) https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1323358024000249

(3) https://arxiv.org/pdf/2406.19029