The Role of Cold Flows and Reservoirs in Galaxy Formation With Strong
  Feedback
  We examine gas accretion and subsequent star formation in representative
galaxies from the McMaster Unbiased Galaxy Simulations (Stinson et al. 2010).
Accreted gas is bimodal with a natural temperature division at $10^5$ K, near
the peak of the cooling curve. Cold-mode accretion dominates inflows at early
times, creating a peak in total accretion at redshift z=2-4 and declining
exponentially below z$\sim$2. Hot-mode accretion peaks near z=1-2 and declines
gradually. Hot-mode exceeds cold-mode accretion at z$\sim$1.8 for all four
galaxies rather than when the galaxy reaches a characteristic mass. Cold-mode
accretion can fuel immediate star formation, while hot-mode accretion
preferentially builds a large, hot gas reservoir in the halo. Late-time star
formation relies on reservoir gas accreted 2-8 Gyr prior. Thus, the reservoir
allows the star formation rate to surpass the current overall gas accretion
rate. Stellar feedback cycles gas from the interstellar medium back into the
hot reservoir. Stronger feedback results in more gas cycling, gas removal in a
galactic outflow and less star formation overall, enabling simulations to match
the observed star formation history. For lower mass galaxies in particular,
strong feedback can delay the star formation peak to z=1-2 from the accretion
peak at z=2-4.
