Improved Searches for HI in Three Dwarf Spheroidal Galaxies

Abstract

Previous searches for HI 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 VLA observations of three dwarf spheroidals: Fornax, Leo II, and Draco, all of which have known stellar velocities. The new data show no HI emission or absorption. Column density limits in emission are 4--7 x 10^18 atoms/cm^2 in the centers of the galaxies. The importance of the new observations is that they cover larger areas than previous searches and they are less plagued by confusion with foreground (Galactic) HI. The apparent absence of neutral gas in the Fornax dwarf spheroidal is especially puzzling because recent photometry shows evidence of stars only 10^8 years old. We discuss whether the VLA observations could have missed significant amounts of HI.

20 pages, 7 figures; to appear in the Astronomical Journal

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• A Wide-Field Survey of the Fornax Dwarf Spheroidal Galaxy
• Star Formation and the ISM in Four Dwarf Irregular Galaxies
• The Chemical Enrichment History of the Fornax Dwarf Spheroidal Galaxy from the Infrared Calcium Triplet
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• Particle Dark Matter Constraints from the Draco Dwarf Galaxy
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• Spitzer Space Telescope spectral observations of AGB stars in the Fornax dwarf spheroidal galaxy
• A Search for Ionized Gas in the Draco and Ursa Minor Dwarf Spheroidal Galaxies
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