The surprising inefficiency of dwarf satellite quenching

Abstract

We study dwarf satellite galaxy quenching using observations from the Geha et al. NASA-Sloan Atlas/SDSS catalogue together with cold dark matter cosmological simulations to facilitate selection and interpretation. We show that fewer than 30 per cent of dwarfs (M 10 8.5-9.5 M ) identified as satellites within massive host haloes (M host 10 12.5-14 M ) are quenched, in spite of the expectation from simulations that half of them should have been accreted more than 6 Gyr ago. We conclude that whatever the action triggering environmental quenching of dwarf satellites, the process must be highly inefficient. We investigate a series of simple, one-parameter quenching models in order to understand what is required to explain the low quenched fraction and conclude that either the quenching time-scale is very long (>9.5 Gyr, a 'slow starvation' scenario) or that the environmental trigger is not well matched to accretion within the virial volume. We discuss these results in light of the fact that most of the low-mass dwarf satellites in the Local Group are quenched, a seeming contradiction that could point to a characteristic mass scale for satellite quenching.