A study of AGN and supernova feedback in simulations of isolated and merging disc galaxies

We perform high-resolution N-body+smoothed particle hydrodynamics simulations of isolated Milky Way-like galaxies and major mergers between them, to investigate the effect of feedback from both an active galactic nucleus (AGN) and supernovae on the galaxy's evolution. Several AGN methods from the literature are used independently and in conjunction with supernova feedback to isolate the most important factors of these feedback processes. We find that in isolated galaxies, supernovae dominate the suppression of star formation but the star formation rate is unaffected by the presence of an AGN. In mergers the converse is true when models with strong AGN feedback are considered, shutting off star formation before a starburst can occur. AGN and supernovae simulated together suppress star formation only slightly more than if they acted independently. This low-level interaction between the feedback processes is due to AGN feedback maintaining the temperature of a hot halo of gas formed by supernovae. For each of the feedback processes, the heating temperature is the dominant parameter rather than the overall energy budget or timing of heating events. Finally, we find that the black hole mass is highly resolution dependent, with more massive black holes found in lower resolution simulations.