Probing Sightlines Through Nearby Galaxies
Session 25 -- QSO Absorption-Line Studies with HST and Keck
Oral presentation, Tuesday, June 13, 1995, 8:30am - 12:30pm

## [25.05] Probing Sightlines Through Nearby Galaxies

David V. Bowen (Space Telescope Science Institute)

We discuss current result from HST regarding the nature of absorbing halos around nearby galaxies. We summarise the conclusions from a survey designed to search for weak Mg~II absorption from present-epoch galaxies using the GHRS. The data show that galaxies do not possess extended Mg~II cross-sections beyond radii of 50~$h^{-1}$~kpc to a column density limit of $\leq\:4\times 10^{12}$~cm$^{-2}$. The covering factor of gas at radii $<\:10$~$h^{-1}$~kpc (and within an optical radius) is high, but the characteristics of the absorption --- the strength and complexity of a line, and the ionization state of the absorbing gas --- depend on the galaxy's environment. There is also evidence that early-type galaxies may not possess the same cross-sections as late-type galaxies.

We present new FOS spectra of QSOs whose sightlines pass through the outer regions of two bright spiral galaxies, beyond the stellar radius of the galaxy but below the radius of Mg~II halos found at $z\:\sim\:0.5$, to study C~IV, Mg~II and Ly$\alpha$ absorption. We also show the far UV spectra of 3C~232, which was the first QSO-galaxy pair studied using ground-based observatories. We conclude by considering the extent of Ly$\alpha$ absorbing halos around nearby galaxies, and how these results compare with higher redshift studies.