How Do Galaxies Get Their Gas?
Most galaxies are actively star forming at all epochs. However, there is not enough gas in galaxies to support evolution of star formation activity over time. This suggests that galactic gas is being replenished from the intergalactic medium.
I use cosmological hydrodynamic simulations to study the
physics of gas supply into galactic component. At high redshift
infall of cold filamentary gas dominates accretion
rates of all galaxies. This "cold mode accretion" differs from the
standard model of galaxy formation in which cooling of the hot halo atmospheres
is a source of galactic gas. Cold mode accretion is a major driver of active
star formation of high-z galaxies enabling such activity to proceed for a significant
fraction of the Hubble time. At low redshift hot virialized gas can cool in some of the halos, but gaseous
clouds that form in infalling filaments bring the
cold gas into galaxies such as Milky Way.
In this talk I will describe properties, physics and consequences of gas accretion processes as well as predictions for a variety of observational probes of cold halo gas that can provide strong constraints on theoretical models. I will also discuss remaining open issues and future directions in studies of galactic gas accretion, including new computational methods and observations with upcoming facilities.