Observing the End of Cold Flow Accretion using Halo Absorption Systems
Abstract
We use cosmological SPH simulations to study the cool, accreted gas in two Milky Way-size galaxies through cosmic time to z=0. We find that gas from mergers and cold flow accretion results in significant amounts of cool gas in galaxy halos. This cool circum-galactic component drops precipitously once the galaxies cross the critical mass to form stable shocks, Mvir = Msh ~ 10^12 Msun. Before reaching Msh, the galaxies experience cold mode accretion (T<10^5 K) and show moderately high covering fractions in accreted gas: f_c ~ 30-50% for R<50 co-moving kpc and N_HI>10^16 cm^-2. These values are considerably lower than observed covering fractions, suggesting that outflowing gas (not included here) is important in simulating galaxies with realistic gaseous halos. Within ~500 Myr of crossing the Msh threshold, each galaxy transitions to hot mode gas accretion, and f_c drops to ~5%. The sharp transition in covering fraction is primarily a function of halo mass, not redshift. This signature should be detectable in absorption system studies that target galaxies of varying host mass, and may provide a direct observational tracer of the transition from cold flow accretion to hot mode accretion in galaxies.
Cite
@article{arxiv.1012.2128,
title = {Observing the End of Cold Flow Accretion using Halo Absorption Systems},
author = {Kyle R. Stewart and Tobias Kaufmann and James S. Bullock and Elizabeth J. Barton and Ariyeh H. Maller and Jürg Diemand and James Wadsley},
journal= {arXiv preprint arXiv:1012.2128},
year = {2011}
}
Comments
6 pages, 2 figures. Minor changes to match published version (results unchanged)