Does supernova feedback regulate the star formation rate in dwarf galaxies?

Abstract

Stars form in cold, dense clouds embedded in galactic discs, but whether their formation is primarily regulated by gravitational collapse, turbulence, or stellar feedback remains unclear. Using four high-resolution dwarf galaxy simulations with and without supernova (SN) feedback and magnetic fields, we test how feedback regulates the supply of dense gas and, consequently, the star formation rate (SFR). Although the SFR does increase when SNe are turned off, this increase is only by a factor of a few. Instead, across all models, the theoretical maximum SFR originally proposed by Zuckerman and Palmer, defined as the ratio of the total dense gas mass to its mean free-fall time (${M_{\rm dense}}/{\tff}$), always exceeds the measured SFR by nearly two orders of magnitude. Moreover, the increase of the SFR in the case without SNe is accompanied by a nearly corresponding increase of the total dense gas mass ($M_{\rm dense}$), such that the dense-gas depletion time, $\tau \equiv {\rm SFR}/M_{\rm dense}$, decreases by only $\sim 33\%$ in the hydrodynamical case and by about 55\% in the magnetohydrodynamical models. This indicates that SN feedback does not primarily act by slowing the collapse of dense gas, but instead by limiting how much diffuse gas can be converted into dense gas. Our results suggest that the main contribution to the regulation of the SFR, at least in dwarf galaxies, may arise from stabilization by galactic rotation, rather than by SN feedback.