The Gas Content and Stripping of Local Group Dwarf Galaxies

Abstract The gas content of the complete compilation of Local Group dwarf galaxies (119 within 2 Mpc) is presented using H i survey data. Within the virial radius of the Milky Way (224 kpc here), 53 of 55 dwarf galaxies are devoid of gas to limits of M H i < 104 M ⊙. Within the virial radius of M31 (266 kpc), 27 of 30 dwarf galaxies are devoid of gas (with limits typically <105 M ⊙). Beyond the virial radii of the Milky Way and M31, the majority of the dwarf galaxies have detected H i gas and H i masses higher than the limits. When the relationship between gas content and distance is investigated using a Local Group virial radius, more of the nondetected dwarf galaxies are within this radius (85 ± 1 of the 93 nondetected dwarf galaxies) than within the virial radii of the Milky Way and M31. Using the Gaia proper-motion measurements available for 38 dwarf galaxies, the minimum gas density required to completely strip them of gas is calculated. Halo densities between 10−5 and 5 × 10−4 cm−3 are typically required for instantaneous stripping at perigalacticon. When compared to halo density with radius expectations from simulations and observations, 80% of the dwarf galaxies with proper motions are consistent with being stripped by ram pressure at Milky Way pericenter. The results suggest that a diffuse gaseous galactic halo medium is important in quenching dwarf galaxies, and that a Local Group medium also potentially plays a role.