Stellar Feedback in Galaxies and the Origin of Galaxy-scale Winds
  Feedback from massive stars is believed to play a critical role in driving
galactic super-winds that enrich the IGM and shape the galaxy mass function and
mass-metallicity relation. In previous papers, we introduced new numerical
methods for implementing stellar feedback on sub-GMC through galactic scales in
galaxy simulations. This includes radiation pressure (UV through IR), SNe
(Type-I & II), stellar winds ('fast' O-star through 'slow' AGB winds), and HII
photoionization. Here, we show that these feedback mechanisms drive galactic
winds with outflow rates as high as ~10-20 times the galaxy SFR. The
mass-loading efficiency (wind mass loss rate divided by SFR) scales inversely
with circular velocity, consistent with momentum-conservation expectations. We
study the contributions of each feedback mechanism to galactic winds in a range
of galaxy models, from SMC-like dwarfs & MW-analogues to z~2 clumpy disks. In
massive, gas-rich systems (local starbursts and high-z galaxies), radiation
pressure dominates the wind generation. For MW-like spirals and dwarf galaxies
the gas densities are much lower, and shock-heated gas from SNe and stellar
winds dominates production of large-scale outflows. In all models, however,
winds have a multi-phase structure that depends on interactions between
multiple feedback mechanisms operating on different spatial & time scales: any
single mechanism fails to reproduce the winds observed. We provide fitting
functions for wind mass-loading and velocities as a function of galaxy
properties, for use in cosmological simulations and semi-analytic models. These
differ from typically-adopted formulae with explicit dependence on gas surface
density that can be very important in both low-density dwarf galaxies and
high-density gas-rich galaxies.
