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T. Robishaw, L. Blitz (University of California at Berkeley)
We present evidence that nearly half of the dwarf spheroidal galaxies (dSph and dSph/dIrr) in the Local Group are associated with large reservoirs of atomic gas, in some cases larger than the stellar mass. The gas is sometimes found at large distance (~10 kpc) from the center of a galaxy and is not necessarily centered on it. The properties of some of the gas reservoirs are similar to the median properties of the High-Velocity Clouds (HVCs); two of the H\rm\scriptstyle I reservoirs are cataloged HVCs. The association of the H\rm\scriptstyle I with the dwarf spheroidals might thus provide a link between the High-Velocity Clouds (HVCs) and stars. We show that the H\rm\scriptstyle I content of the Local Group dSphs and dIrrs exhibits a sharp decline if the galaxy is within 250 kpc of either the Milky Way or M31. This suggests that each galaxy has a massive (1010\, \rm M\odot) x-ray emitting halo that produces ram-pressure stripping if a dwarf ventures too close to either giant spiral. For the derived mean density of the hot gas, n\circ = 2.5 \times 10-5\ \rm cm-3, ram-pressure stripping is found to be more than an order of magnitude more effective than tidal stripping in removing the gas from the dSph galaxies.
This research was partially supported by the National Science Foundation.
The author(s) of this abstract have provided an email address for comments about the abstract: robishaw@astro.umd.edu