Gusty, gaseous flows of FIRE: galactic winds in cosmological simulations
  with explicit stellar feedback
  We present an analysis of the galaxy-scale gaseous outflows from the FIRE
(Feedback in Realistic Environments) simulations. This suite of hydrodynamic
cosmological zoom simulations resolves formation of star-forming giant
molecular clouds to $z=0$, and features an explicit stellar feedback model on
small scales. Our simulations reveal that high redshift galaxies undergo bursts
of star formation followed by powerful gusts of galactic outflows that eject
much of the ISM and temporarily suppress star formation. At low redshift,
however, sufficiently massive galaxies corresponding to L*-progenitors develop
stable disks and switch into a continuous and quiescent mode of star formation
that does not drive outflows far into the halo. Mass-loading factors for winds
in L*-progenitors are $\eta \approx 10$ at high redshift, but decrease to $\eta
\ll 1$ at low redshift. Although lower values of $\eta$ are expected as halos
grow in mass over time, we show that the strong suppression of outflows with
decreasing redshift cannot be explained by mass evolution alone. Circumgalactic
outflow velocities are variable and broadly distributed, but typically range
between one and three times the circular velocity of the halo. Much of the
ejected material builds a reservoir of enriched gas within the circumgalactic
medium, some of which could be later recycled to fuel further star formation.
However, a fraction of the gas that leaves the virial radius through galactic
winds is never regained, causing most halos with mass $M_h \le 10^{12}
M_{\odot}$ to be deficient in baryons compared to the cosmic mean by $z=0$.
