Stellar Feedback in Galaxies and the Origin of Galaxy-scale Winds

TLDR: In this paper, the authors have introduced new numerical methods for implementing stellar feedback on sub-GMC through galactic scales in numerical simulations of galaxies; the key physical processes include radiation pressure in the UV through IR, supernovae (Type-I & II), stellar winds (fast O star through “slow” AGB winds), and HII photoionization.

Abstract: Feedback from massive stars is believed to play a critical role in driving galactic superwinds that enrich the intergalactic medium and shape the galaxy mass function, massmetallicity relation, and other global galaxy properties. In previous papers, we have introduced new numerical methods for implementing stellar feedback on sub-GMC through galactic scales in numerical simulations of galaxies; the key physical processes include radiation pressure in the UV through IR, supernovae (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 star formation rate. The mass-loading efficiency (wind mass loss rate divided by the star formation rate) scales roughly as _ Mwind= _ M / V 1 c (where Vc is the galaxy circular velocity), consistent with simple momentum-conservation expectations. We use our suite of simulations to study the relative contribution of each feedback mechanism to the generation of galactic winds in a range of galaxy models, from SMC-like dwarfs and Milky-way analogues to z 2 clumpy disks. In massive, gas-rich systems (local starbursts and high-z galaxies), radiation pressure dominates the wind generation. By contrast, for MW-like spirals and dwarf galaxies the gas densities are much lower and sources of shock-heated gas such as supernovae and stellar winds dominate the production of large-scale outflows. In all of our models, however, the winds have a complex multi-phase structure that depends on the interaction between multiple feedback mechanisms operating on different spatial and time scales: any single feedback mechanism fails to reproduce the winds observed. We use our simulations to provide fitting functions to the 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 an explicit dependence on the gas surface density that can be very important in both low-density dwarf galaxies and high-density gas-rich galaxies.