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, $τ\equiv {\rm SFR}/M_{\rm dense}$, 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.

Figures (13)

• Figure 1: The mass weighted cell radius against number density for each of the simulations taken at the last snapshot. The dashed vertical line represents the sink creation density threshold. We can see here the increase in hyper refined cells in the models without supernova feedback.
• Figure 2: The HI gas surface density projections for each of the four models used in the analysis. The top row shows the hydrodynamical models, the bottom row shows the MHD models. On the left we show the models with SNe feedback, the right column has no SNe feedback. The dense filament structures that form due to self-gravity when there is no support from feedback in the gas can be clearly seen.
• Figure 3: Integrated temperature projection of the 4 models. The diffuse voids seen in the SNe models in Figure \ref{['fig:SD']} are seen as hot bright spots. Whereas the voids in the models without SNe are more consistent with the diffuse gas.
• Figure 4: The total gas (dashed line) and dense gas (solid line) surface density radial profiles for the MHD (blue) and Hydro (red) simulations with and without SNe averaged over the steady-state period.
• Figure 5: The strength of the magnetic field with the field line structure over plotted in the two MHD models presented in this work. The left plot is the model with SNe feedback, the right has no SNe. It is clear in these plots that without feedback the resulting field is more organised and evenly distributed across the disc.