Superbubble Feedback in Galaxy Formation

Abstract: We present new work on galactic feeback. Our new superbubble-based stellar feedback (Keller et al 2014) is due to clustered young stars. It evolves differently to individual supernovae. A hot superbubble phase is required to correctly accumulate feedback from multiple, clustered sources, including stellar winds and supernovae. The model requires thermal conduction, sub-grid evaporation and a temporary multi-phase treatment at lower resolution. Thermal conduction physically sets the hot gas mass associated with feedback and outflows (thus mass loading is not a free parameter as in other models). Prior approaches often heat too much mass, leaving the hot ISM below 10^6 K and susceptible to rapid cooling without ad-hoc fixes. High resolution single star cluster simulations are used to show insensitivity to resolution and ISM conditions. The model produces a Kennicutt-Schmidt star formation rate law and strong outflows in SPH simulations of Milky Way and dwarf galaxy analogues and regulates cosmological star formation to the observed levels. We discuss general implications for numerical treatements of feedback and prospects for curtailing the embarassingly high number of free parameters in galaxy formation models today.