The Gas Content and Stripping of Local Group Dwarf Galaxies

TL;DR

This study analyzes the gas content of 119 Local Group dwarf galaxies, finding most are gas-depleted within the virial radii of the Milky Way and M31, and suggests ram pressure stripping by halo gas is a key quenching mechanism.

Contribution

It provides a comprehensive analysis of gas content in Local Group dwarfs using HI data and Gaia proper motions, highlighting the role of halo density in gas stripping.

Findings

Most dwarf galaxies within virial radii are gas-depleted.

Ram pressure stripping by halo gas explains gas loss in dwarfs.

A diffuse gaseous halo likely quenches star formation in dwarfs.

Abstract

The gas content of the complete compilation of Local Group dwarf galaxies (119 within 2 Mpc) is presented using HI 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$_{\rm HI}<10^4$ M$_\odot$. Within the virial radius of M31 (266 kpc), 27 of 30 dwarf galaxies are devoid of gas (with limits typically $<10^5$ M$_\odot$). Beyond the virial radii of the Milky Way and M31, the majority of the dwarf galaxies have detected HI gas and have HI masses higher than the limits. When the relationship between gas content and distance is investigated using a Local Group virial radius, more of the non-detected dwarf galaxies are within this radius (85$\pm1$ of the 93 non-detected 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 $5 \times 10^{-4}$ 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 a diffuse gaseous galactic halo medium is important in quenching dwarf galaxies, and that a Local Group medium also potentially plays a role.