Gas depletion in local group dwarfs on 250kpc scales: Ram pressure stripping assisted by internal heating at early times

Abstract

A recent survey of the Galaxy and M31 reveals that more than 90% of dwarf galaxies within 270kpc of their host galaxy are deficient in H I gas. At such an extreme radius, the coronal halo gas is an order of magnitude too low to remove H I gas through ram pressure stripping for any reasonable orbit distribution. However, all dwarfs are known to have an ancient stellar population (≳ 10 Gyr) from early epochs of vigorous star formation which, through heating of H I, could allow the hot halo to remove this gas. Our model looks at the evolution of these dwarf galaxies analytically as the host-galaxy dark matter halo and coronal halo gas build up over cosmic time. The dwarf galaxies - treated as spherically symmetric, smooth distributions of dark matter and gas - experience early star formation, which sufficiently heats the gas, allowing it to be removed easily through tidal stripping by the host galaxy, or ram pressure stripping by a tenuous hot halo (n H = 3 × 10-4 cm-3 at 50kpc). This model of evolution is able to explain the observed radial distribution of gas-deficient and gas-rich dwarfs around the Galaxy and M31 if the dwarfs fell in at high redshift (z 3-10). © 2011. The American Astronomical Society. All rights reserved.