Taking care of business in a flash : constraining the time-scale for low-mass satellite quenching with ELVIS

Abstract

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 ELVIS suite of N -body simulations to constrain the characteristic timescale 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 timescale (∼ 2 Gyr) for dwarf satellites in the mass range M ∼ 10 6 − 10 8 M . This quenching timescale 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 halos, suggesting a dramatic change in the dominant satellite quenching mechanism at M 10 8 M . Combining our work with the results of complementary analyses in the literature, we conclude that the suppression of star formation in massive satellites (M ∼ 10 8 − 10 11 M ) is broadly consistent with being driven by starvation, such that the satellite quenching timescale corresponds to the cold gas depletion time. Below a critical stellar mass scale of ∼ 10 8 M , however, the required quenching times are much shorter than the expected cold gas depletion times. Instead, quenching must act on a timescale comparable to the dynamical time of the host halo. We posit that ram-pressure stripping can naturally explain this behavior, with the critical mass (of M ∼ 10 8 M ) corresponding to halos with gravitational restoring forces that are too weak to overcome the drag force encountered when moving through an extended, hot circumgalactic medium.

Under pressure: quenching star formation in low-mass satellite galaxies via stripping

“…For satellites with M 10 8 M , the long quenching timescales inferred from the relatively low observed satellite quenched fractions are consistent with starvation as the dominant quenching mechanism (Fillingham et al 2015, see also Davies et al 2016 Figure 6. The fraction of HI gas stripped (f stripped ) via ram-pressure and turbulent viscous stripping as a function of satellite stellar mass for our sample of 66 dwarf galaxies.…”

“…As illustrated by Fillingham et al (2015), the measured satellite quenching timescales at high masses, including the lack of strong dependence on host halo mass, are broadly consistent with the expectations for quenching via starvation (see also van den Bosch et al 2008;Wetzel et al 2013). At low masses, on the other hand, the short quenching timescales inferred from analysis of the Local Group satellite population are difficult to fully explain.…”

“…quenched fractions observed in the Local Group require a very short quenching timescale, consistent with a physical process that acts on roughly the dynamical time, such as ram-pressure stripping (Wetzel, Tollerud & Weisz 2015;Fillingham et al 2015). While stripping, and in particular rampressure stripping, is often thought to be a possible factor in the dearth of star-forming dwarfs in the Local Group (Einasto et al 1974;Lin & Faber 1983;Blitz & Robishaw 2000), these recent results provide possible benchmarks by which to measure stripping as an active quenching mechanism.…”

“…While ram-pressure stripping acts at the correct mass scales, our analysis finds that ram pressure alone is unable to suppress star formation in infalling satellites on the timescales predicted by Fillingham et al (2015). As shown in Fig.…”

“…2 Gyr, Fillingham et al 2015). Approximately 50% (or 55%) of the subhalo population in ELVIS reaches pericenter (or 0.5 Rvir) within ∼ 1.5 Gyr (or ∼ 1 Gyr) of infall, where instantaneous ram-pressure stripping is assumed to occur.…”