Superbubble Feedback in Galaxy Evolution

Abstract

Galaxy formation is a complex, nonlinear process that occurs over scales that span orders of magnitude in space and time. Of the many phenomena taking place within a galaxy, supernovae (SN) are among the most important. SN heat, stir, and eject gas from the galaxy. This has profound impact on the galaxy's evolution over cosmic time. Numerical simulations of galaxies must often include models for feedback from SN. We present a new model for SN feedback that captures the effects of previously ignored physics: thermal conduction. Massive stars form in clusters, allowing their SN ejecta to merge into a superbubble, which can vent from the disc to drive a high-entropy galactic outflow. Thermal conduction determines how much mass is mixed into this superbubble.

We use this to study SN feedback in galaxy evolution, and come to four major conclusions. First, superbubbles drive stronger galactic outflows in compared to past models of SN feedback. Second, these outflows are key to both preventing the overproduction of stars and the formation of too-massive central bulges. High redshift outflows eject starforming gas, and preferentially remove bulge forming gas. Third, we show that SN cannot prevent runaway star formation in galaxies more massive than our own $(M_{halo}>10^{12}\;\rm{M_\odot})$. In these galaxies, SN are unable to prevent transport of gas towards the centre of the galaxy. These results suggest a transition between regulation from stars to regulation from supermassive black holes occurs at roughly this mass. Finally, we use our simulated galaxies to show recent observations of the Radial Acceleration Relation (RAR) are consistent with $\Lambda$CDM cosmology. The RAR ties galaxy kinematics to baryonic mass, in a tight, universal scaling relation. While this has been claimed as potential evidence of exotic new physics, we show this same tight relation occurs for galaxies formed in $\Lambda$CDM.