2015MNRAS.454.2039F

The vast majority of dwarf satellites orbiting the Milky Way and M31 are quenched, while comparable galaxies in the field are gas rich and star forming. Assuming that this dichotomy is driven by environmental quenching, we use the Exploring the Local Volume in Simulations (ELVIS) suite of N-body simulations to constrain the characteristic time-scale upon which satellites must quench following infall into the virial volumes of their hosts. The high satellite quenched fraction observed in the Local Group demands an extremely short quenching time-scale ( ∼ 2 Gyr) for dwarf satellites in the mass range M{sstarf} ∼ 10⁶-10⁸M_☉. This quenching time-scale is significantly shorter than that required to explain the quenched fraction of more massive satellites ( ∼ 8 Gyr), both in the Local Group and in more massive host haloes, suggesting a dramatic change in the dominant satellite quenching mechanism at M{sstarf} ≲ 10⁸M_☉. Combining our work with the results of complementary analyses in the literature, we conclude that the suppression of star formation in massive satellites (M{sstarf} ∼ 10⁸-10¹¹M_☉) is broadly consistent with being driven by starvation, such that the satellite quenching time-scale corresponds to the cold gas depletion time. Below a critical stellar mass scale of ∼ 10⁸M_☉, however, the required quenching times are much shorter than the expected cold gas depletion times. Instead, quenching must act on a time-scale comparable to the dynamical time of the host halo. We posit that ram-pressure stripping can naturally explain this behaviour, with the critical mass (of M{sstarf} ∼ 10⁸M_☉) corresponding to haloes with gravitational restoring forces that are too weak to overcome the drag force encountered when moving through an extended, hot circumgalactic medium.