The Gaseous Trail of the Sagittarius Dwarf Galaxy

Abstract

A possible gaseous component to the stream of debris from the Sagittarius dwarf galaxy is presented. We identify 4 - 10 x 10^6 Msun of neutral hydrogen along the orbit of the Sgr dwarf in the direction of the Galactic anticenter (at 36 kpc, the distance to the stellar debris in this region). This is 1-2% of the estimated total mass of the Sgr dwarf. Both the stellar and gaseous components have negative velocities, but the gaseous component extends to higher negative velocities. If associated, this gaseous stream was most likely stripped from the main body of the dwarf 0.2 - 0.3 Gyr ago during its current orbit after a passage through a diffuse edge of the Galactic disk with a density > 10^{-4} cm^{-3}. This gas represents the dwarf's last source of star formation fuel and explains how the galaxy was forming stars 0.5-2 Gyr ago.