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

Mon. Not. R. Astron. Soc. 000, 1–12 (2015) Printed 27 August 2015 (MN L A TEX style file v2.2) Taking Care of Business in a Flash E: Constraining the Timescale for Low-Mass Satellite Quenching with ELVIS arXiv:1503.06803v2 [astro-ph.GA] 25 Aug 2015 Sean P. Fillingham, 1? Michael C. Cooper, 1 † Coral Wheeler, 1 Shea Garrison-Kimmel, 1 Michael Boylan-Kolchin, 2 James S. Bullock 1 Center for Cosmology, Department of Physics and Astronomy, 4129 Reines Hall, University of California, Irvine, CA 92697 of Astronomy and Joint Space-Science Institute, University of Maryland, College Park, MD 20742-2421 2 Department 27 August 2015 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. Key words: Local Group – galaxies: formation – galaxies: evolution – galaxies: dwarf – galaxies: star formation INTRODUCTION Foremost among the results of galaxy surveys over the last decade has been the realization that the galaxy population at z . 2 is bimodal in nature (e.g. Strateva et al. 2001; Baldry et al. 2004; Bell et al. 2004; Cooper et al. 2006). That is, galaxies both locally and out to intermediate red- shift are effectively described as one of two distinct types: red, early-type galaxies lacking significant star formation and blue, late-type galaxies with active star formation. In color-magnitude space, the red galaxies populate a tight re- lation (often called the red sequence), while the distribu- tion of blue galaxies is more scattered (sometimes referred to as the blue cloud). While the red and blue populations ? e-mail: sfilling@uci.edu † e-mail: cooper@uci.edu c 2015 RAS comprise approximately equal portions of the cosmic stellar mass budget at z ∼ 1, galaxies on the red sequence domi- nate today, following a growth in stellar mass within the red population of roughly a factor of 2 over the past 7 Gyr (Bell et al. 2004; Bundy et al. 2006; Faber et al. 2007; Brown et al. 2007). Despite uncertainty regarding the particular physical process(es) at play, the suppression (or quenching) of star formation in blue galaxies, thereby making them red, is one of the principal drivers of this dramatic growth in the num- ber density of quiescent systems at late cosmic time. At both low and intermediate redshift, the local envi- ronment of a galaxy is known to be well-correlated with the suppression of star formation, such that passive or quies- cent galaxies preferentially live in higher-density environ- ments (Balogh et al. 2004; Kauffmann et al. 2004; Blanton et al. 2005; Cooper et al. 2006, 2007, 2010a). While the stel-