The evolution of galaxies' multi-phase gas reservoirs by environment

Over the last decade in particular, our understanding of the effect of environment on galaxies' cold-gas reservoirs has blossomed. There is a clear picture from 21-cm observations and cosmological simulations that low-redshift satellite galaxies have less atomic gas relative to centrals of the same stellar mass, especially in haloes of higher mass. But debate and uncertainty remains about the impact of environment on molecular and ionized gas, which we are also more reliant on at redshifts>0.3. In this talk, I will provide an overview of what current observations tell us about the multi-phase gas reservoirs of galaxies across cosmic time and environments, comparing and contrasting to the latest predictions from cosmological simulations, including IllustrisTNG. This is a critical topic for this conference's section on "Galaxies across time". I will highlight where the most significant tension between theory and observation lie, and where the largest sources of uncertainty in comparing the two come from. Finally, I will touch on how upcoming surveys like WALLABY and VERTICO, as well as the Genesis simulation program, should help to address some of this tension.