The lives and deaths of faint satellite galaxies around M31

Abstract We present predictions for proper motions, infall times and times of first pericentric passage for 39 of M31’s satellite galaxies. We estimate these by sampling satellite orbits from cosmological N-body simulations matched on mass, distance and velocity along the line of sight, in addition to properties of the host system. Our predictions are probabilistic based on repeated sampling from the uncertainty distributions of all quantities involved. We use these constraints on the satellites’ orbital histories in conjunction with their published star formation histories to investigate the dominant environmental mechanisms for quenching satellites of M31-like hosts. Around half of the satellites appear to have quenched before their first pericentric passage around M31. Only the most massive satellites (with stellar masses >108M⊙) are able to maintain star formation for up to billions of years after infall. The majority of faint satellites, with M⋆ < 108 M⊙, were likely quenched before entering the M31 system. We compare our results for M31 against predictions for the Milky Way’s satellites from the literature; M31’s has a more active recent accretion history with more recently quenched satellites than the Milky Way.