In-N-Out: the gas cycle from dwarfs to spiral galaxies

We examine the scalings of galactic outflows with halo mass across a suite of twenty high-resolution cosmological zoom galaxy simulations covering halo masses from 10^9.5 - 10^12 M_sun. These simulations self-consistently generate outflows from the available supernova energy in a manner that successfully reproduces key galaxy observables including the stellar mass-halo mass, Tully-Fisher, and mass-metallicity relations. We quantify the importance of ejective feedback to setting the stellar mass relative to the efficiency of gas accretion and star formation. Ejective feedback is increasingly important as galaxy mass decreases; we find an effective mass loading factor that scales as v_circ^(-2.2), with an amplitude and shape that is invariant with redshift. These scalings are consistent with analytic models for energy-driven wind, based solely on the halo potential. Recycling is common: about half the outflow mass across all galaxy masses is later re-accreted. The recycling timescale is typically about 1 Gyr, virtually independent of halo mass. Recycled material is re-accreted farther out in the disk and with typically about 2-3 times more angular momentum. These results elucidate and quantify how the baryon cycle plausibly regulates star formation and alters the angular momentum distribution of disk material across the halo mass range where most of cosmic star formation occurs.