Characterizing mass, momentum, energy and metal outflow rates of
  multi-phase galactic winds in the FIRE-2 cosmological simulations
  We characterize mass, momentum, energy and metal outflow rates of multi-phase
galactic winds in a suite of FIRE-2 cosmological "zoom-in" simulations from the
Feedback in Realistic Environments (FIRE) project. We analyze simulations of
low-mass dwarfs, intermediate-mass dwarfs, Milky Way-mass halos, and
high-redshift massive halos. Consistent with previous work, we find that dwarfs
eject about 100 times more gas from their interstellar medium (ISM) than they
form in stars, while this mass "loading factor" drops below one in massive
galaxies. Most of the mass is carried by the hot phase ($>10^5$ K) in massive
halos and the warm phase ($10^3-10^5$ K) in dwarfs; cold outflows ($<10^3$ K)
are negligible except in high-redshift dwarfs. Energy, momentum and metal
loading factors from the ISM are of order unity in dwarfs and significantly
lower in more massive halos. Hot outflows have $2-5\times$ higher specific
energy than needed to escape from the gravitational potential of dwarf halos;
indeed, in dwarfs, the mass, momentum, and metal outflow rates increase with
radius whereas energy is roughly conserved, indicating swept up halo gas.
Burst-averaged mass loading factors tend to be larger during more powerful star
formation episodes and when the inner halo is not virialized, but we see
effectively no trend with the dense ISM gas fraction. We discuss how our
results can guide future controlled numerical experiments that aim to elucidate
the key parameters governing galactic winds and the resulting associated
preventative feedback.
