Real or not real? What cosmological simulations can (and cannot) tell us about the cold phase of the CGM

Wednesday September 30th 2020 @12pm, Zoom Colloquium
Dr Lilian Garratt-Smithson University of Western Australia

Email: lilian.garratt-smithson[at]


Simulations are now allowing us to probe the scales of the CGM (circumgalactic medium) around galaxies in order to look at the influence of realistic galaxy formation processes. However, it is apparent that the properties of the multi-phase CGM are not yet converged in simulations (e.g. Van de Voort et al., 2019; Hummels et al., 2019), hence their reliability to make predictions is still in question. It is also clear the CGM plays a key role in the evolution of a galaxy; it is a supply of gas for star formation and a key site for feedback-generated outflows, along with the recycling of baryons (for a recent review see Tumlinson et al., 2017).

During this talk I will discuss the results of my recent paper (Garratt-Smithson et al. 2020 – available on astro-ph) and in particular the significant mass of HI seen in the CGM of EAGLE galaxies between redshift 2 and 0. I will explore the physical conditions of this HI, and discuss whether or not we can constrain the fraction existing in the cold neutral medium. I will also discuss the physical processes we can constrain by studying the detailed properties of this CGM HI gas; in particular I link my results back to AGN and stellar feedback, along with how this is modelled in simulations. Finally, I will discuss my current projects, which aim to explore the CGM in greater detail using a mix of idealised and cosmological zoom simulations.