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arXiv · 1012.2128

Observing the End of Cold Flow Accretion using Halo Absorption Systems

Kyle R. Stewart·Tobias Kaufmann·James S. Bullock·Elizabeth J. Barton·Ariyeh H. Maller·Jürg Diemand·James Wadsley
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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.

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Kyle R. Stewart, Tobias Kaufmann, James S. Bullock, Elizabeth J. Barton, Ariyeh H. Maller, Jürg Diemand, James Wadsley. 2011-06-06. Observing the End of Cold Flow Accretion using Halo Absorption Systems. https://doi.org/10.1088/2041-8205%2F735%2F1%2Fl1

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