Self-Regulated Star Formation in Galaxies via Momentum Input from
  Massive Stars
  Feedback from massive stars is believed to play a critical role in shaping
the galaxy mass function, the structure of the interstellar medium (ISM), and
the low efficiency of star formation, but the exact form of the feedback is
uncertain. In this paper, the first in a series, we present and test a novel
numerical implementation of stellar feedback resulting from momentum imparted
to the ISM by radiation, supernovae, and stellar winds. We employ a realistic
cooling function, and find that a large fraction of the gas cools to <100K, so
that the ISM becomes highly inhomogeneous. Despite this, our simulated galaxies
reach an approximate steady state, in which gas gravitationally collapses to
form giant molecular clouds (GMCs), dense clumps, and stars; subsequently,
stellar feedback disperses the GMCs, repopulating the diffuse ISM. This
collapse and dispersal cycle is seen in models of SMC-like dwarfs, the
Milky-Way, and z~2 clumpy disk analogues. The simulated global star formation
efficiencies are consistent with the observed Kennicutt-Schmidt relation.
Moreover, the star formation rates are nearly independent of the numerically
imposed high-density star formation efficiency, density threshold, and density
scaling. This is a consequence of the fact that, in our simulations, star
formation is regulated by stellar feedback limiting the amount of very dense
gas available for forming stars. In contrast, in simulations without stellar
feedback, i.e. under the action of only gravity and gravitationally-induced
turbulence, the ISM experiences runaway collapse to very high densities. In
these simulations without feedback, the global star formation rates exceed
observed galactic star formation rates by 1-2 orders of magnitude,
demonstrating that stellar feedback is crucial to the regulation of star
formation in galaxies.
