BARYONS MATTER: WHY LUMINOUS SATELLITE GALAXIES HAVE REDUCED CENTRAL MASSES

Abstract

Using high resolution cosmological hydrodynamical simulations of Milky\nWay-massed disk galaxies, we demonstrate that supernovae feedback and tidal\nstripping lower the central masses of bright (-15 < M_V < -8) satellite\ngalaxies. These simulations resolve high density regions, comparable to giant\nmolecular clouds, where stars form. This resolution allows us to adopt a\nprescription for H_2 formation and destruction that ties star formation to the\npresence of shielded, molecular gas. Before infall, supernova feedback from the\nclumpy, bursty star formation captured by this physically motivated model leads\nto reduced dark matter (DM) densities and shallower inner density profiles in\nthe massive satellite progenitors (Mvir > 10^9 Msun, Mstar > 10^7 Msun)\ncompared to DM-only simulations. The progenitors of the lower mass satellites\nare unable to maintain bursty star formation histories, due to both heating at\nreionization and gas loss from initial star forming events, preserving the\nsteep inner density profile predicted by DM-only simulations. After infall,\ntidal stripping acts to further reduce the central densities of the luminous\nsatellites, particularly those that enter with cored dark matter halos,\nincreasing the discrepancy in the central masses predicted by baryon+DM and\nDM-only simulations. We show that DM-only simulations, which neglect the\nbaryonic effects described in this work, produce denser satellites with larger\ncentral velocities. We provide a simple correction to the central DM mass\npredicted for satellites by DM-only simulations. We conclude that DM-only\nsimulations should be used with great caution when interpreting kinematic\nobservations of the Milky Way's dwarf satellites.\n