The Absence of Di use Gas around the Dwarf

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 ? 4 kpc of the galaxy is N(H I) < 10 17 cm ?2 ; assuming that the high ionization lines of Si IV and C IV dominate the ionization fraction of silicon and carbon, then the limit to the total hydrogen column is N(H) < 10 18 cm ?2. Our results demonstrate that there are no dense ows 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 insuucient to rule out the existence of a sphere or shell of ionized gas around { 2 { the dSph, with a mass up to that constituting the entire galaxy. Our models show that dSph galaxies similar to Leo I are not massive enough to have halos which can contribute signiicantly to the metal line absorption cross-section of QSO absorbers seen at high redshift.