Rapid Environmental Quenching of Satellite Dwarf Galaxies in the Local Group

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In the Local Group, nearly all of the dwarf galaxies (Mₛtar < 10⁹ Mₛun) that are satellites within 300 kpc (the virial radius) of the Milky Way (MW) and Andromeda (M31) have quiescent star formation and little-to-no cold gas. This contrasts strongly with comparatively isolated dwarf galaxies, which are almost all actively star-forming and gas-rich. This near dichotomy implies a rapid transformation of satellite dwarf galaxies after falling into the halos of the MW or M31. We combine the observed quiescent fractions for satellites of the MW and M31 with the infall times of satellites from the Exploring the Local Volume in Simulations (ELVIS) suite of cosmological zoom-in simulations to determine the typical timescales over which environmental processes within the MW/M31 halos remove gas and quench star formation in low-mass satellite galaxies. The quenching timescales for satellites with Mₛtar < 10⁸ Mₛun are short, < 2 Gyr, and quenching is more rapid at lower Mₛtar. These satellite quenching timescales can be 1 - 2 Gyr longer if one includes the time that satellites were environmentally preprocessed by low-mass groups prior to MW/M31 infall. We compare with quenching timescales for more massive satellites from previous works to synthesize the nature of satellite galaxy quenching across the observable range of Mₛtar = 10³⁻¹¹ Mₛun. The satellite quenching timescale increases rapidly with satellite Mₛtar, peaking at 9.5 Gyr for Mₛtar 10⁹ Mₛun, and the timescale rapidly decreases at higher Mₛtar to < 5 Gyr at Mₛtar > 5 x 10⁹ Mₛun. Overall, galaxies with Mₛtar 10⁹ Mₛun, similar to the Magellanic Clouds, exhibit the longest quenching timescales, regardless of environmental or internal mechanisms.