Cosmic-Ray Feedback from Supernovae in a Parker-unstable Medium

Abstract Supernova energy drives interstellar medium (ISM) turbulence and can help launch galactic winds. What difference does it make if 10% of the energy is initially deposited into cosmic rays? To help answer this question and study cosmic-ray feedback, we perform galactic patch simulations of a stratified ISM in a low star formation rate, high magnetic field regime. We compare two magnetohydrodynamic and cosmic-ray simulations, which are identical except for how each supernova’s energy is injected. In one, 10% of the energy is injected as cosmic-ray energy. In the other case, energy injection is strictly thermal and kinetic. We find that cosmic-ray injections drive a faster, hotter, and more massive outflow long after the injections occur. Both simulations show the formation of cold clouds (with a total mass fraction > 50%) through the Parker instability and thermal instability. The Parker instability simultaneously produces high mass loading factors η > 10 3 as it does not directly require star formation and supernovae. We also show how the Parker instability naturally leads to a decorrelation of cosmic-ray pressure and gas density. This decorrelation leads to a significant decrease in the calorimetric fraction for injected cosmic rays, but it depends on having a highly resolved magnetic field.