WEDNESDAY, October 21
Astronomy Seminar, 2:00 PM - 3:00 PM, 312 Cahill
"How do galaxies get their gas?" Dusan Keres, ITC Fellow at the CfA.

Abstract: 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.