Special TAPIR Seminar
Wednesday, October 21, 2:00pm, 312 Cahill

Dusan Keres, CfA, Harvard

"How do galaxies get their gas?"

Most galaxies are actively star forming at all epochs. However, observations of cold gas reservoirs
indicate that, at any epoch, there is not enough gas in dense galactic component to support evolution
of star formation activity over time. This suggests that galactic gas is being replenished from the
intergalactic medium. I use fully cosmological simulations of galaxy formation to study the gas supply
into galactic component from high redshift to present. At high redshift "smooth" infall of cold filamentary
gas dominates the gas supply of all galaxies. This "cold mode accretion" is a major driver of very active
star formation of high-z galaxies enabling such activity to proceed for a significant fraction of Hubble
time. Gas accretion rates at a given halo and galaxy mass decrease with time, causing the drop in star
formation rates. Properties and geometry of infalling gas change with halo mass and redshift. At low
redshift some of the halos are able to cool hot virialized gas but filaments are still indirectly supplying
galaxies with gas via cold gaseous clouds that form from infaling cold/warm filamentary gas. In this talk
I will describe properties, physics and consequences of gas accretion, and feedback processes needed
to modulate growth of galaxies over time. Finally, I will point out promising directions for future research
in this area and discuss several observational probes of cold halo gas that can provide strong constraints
on the physics of gas accretion in galaxies.