The impact of feedback on cosmological gas accretion
  We investigate how the way galaxies acquire their gas across cosmic time in
cosmological hydrodynamic simulations is modified by a comprehensive physical
model for baryonic feedback processes. To do so, we compare two simulations --
with and without feedback -- both evolved with the moving mesh code AREPO. The
feedback runs implement the full physics model of the Illustris simulation
project, including star formation driven galactic winds and energetic feedback
from supermassive blackholes. We explore: (a) the accretion rate of material
contributing to the net growth of galaxies and originating directly from the
intergalactic medium, finding that feedback strongly suppresses the raw, as
well as the net, inflow of this "smooth mode" gas at all redshifts, regardless
of the temperature history of newly acquired gas. (b) At the virial radius the
temperature and radial flux of inflowing gas is largely unaffected at z=2.
However, the spherical covering fraction of inflowing gas at 0.25 rvir
decreases substantially, from more than 80% to less than 50%, while the rates
of both inflow and outflow increase, indicative of recycling across this
boundary. (c) The fractional contribution of smooth accretion to the total
accretion rate is lower in the simulation with feedback, by roughly a factor of
two across all redshifts. Moreover, the smooth component of gas with a cold
temperature history, is entirely suppressed in the feedback run at z<1. (d) The
amount of time taken by gas to cross from the virial radius to the galaxy --
the "halo transit time" -- increases in the presence of feedback by a factor of
~2-3, and is notably independent of halo mass. We discuss the possible
implications of this invariance for theoretical models of hot halo gas cooling.
