X iv : a st ro - p h / 96 08 18 9 v 3 2 2 O ct 1 99 6 The Absence of Diffuse Gas around the Dwarf Spheroidal Galaxy Leo

We have obtained spectra of three QSO/AGNs with the GHRS aboard the Hubble Space Telescope to search for absorption from low column density gas in the halo of the dwarf spheroidal (dSph) galaxy Leo I. The probe sightlines pass 2.1, 3.7, and 8.1 kpc from the center of the galaxy, but no C IV, Si II, or Si IV absorption is found at the velocity of Leo I. The absence of low ionization species suggests that the column density of neutral hydrogen which exists within 2− 8 kpc of the galaxy is N(H I) < ∼ 10 cm; assuming that the high ionization lines of Si IV and C IV dominate the ionization fraction of silicon and carbon, the limit to the total hydrogen column is N(H) < ∼ 10 cm. Our results demonstrate that there are no dense flows of gas in or out of Leo I, and that there is no evidence for tidally disrupted gas which might have accompanied the galaxy’s formation or evolution. However, our detection limits are insufficient to rule out the existence of a sphere or shell of ionized gas around Based on observations obtained with the NASA/ESA Hubble Space Telescope, obtained at STScI, which is operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Aeronautics and Space Administration, NAS5-26555. Present address: ST-ECF, ESO, Karl-Schwarzschild-Strasse 2, D-85748, Garching bei München, Germany Currently on leave of absence at the Departmento de Astronomia, Universidad de Guanajuato, Apdo. Postal 144, Guanajuato, C. P. 36000, Mexico