Searches for HI in the Outer Parts of Four Dwarf Spheroidal Galaxies

Previous searches for atomic gas in our Galaxy’s dwarf spheroidal companions have not been complete enough to settle the question of whether or not these galaxies have HI, especially in their outer parts. We present new observations of the dwarf spheroidals Sextans, Leo I, Ursa Minor, and Draco, using the NRAO 140-foot telescope to search much farther in radius than has been done before. The new data go out to at least 2.5 times the core radius in all cases, and well beyond even the tidal radius in two cases. These observations give HI column density limits of 2-6 x 10^17 atoms cm^-2. Unless HI is quite far from the galaxies’ centers, we conclude that these galaxies don’t contain significant amounts of atomic gas at the present time. We discuss whether the observations could have missed some atomic gas.