The Gaseous Extent of Galaxies and the Origin of Ly$\alpha$ Absorption Systems
Session 25 -- QSO Absorption-Line Studies with HST and Keck
Oral presentation, Tuesday, June 13, 1995, 8:30am - 12:30pm

## [25.07] The Gaseous Extent of Galaxies and the Origin of Ly$\alpha$ Absorption Systems

Kenneth M. Lanzetta (State University of New York at Stony Brook)

Latest results of an ongoing imaging and spectroscopic survey of faint galaxies in fields of Hubble Space Telescope spectroscopic target QSOs are presented. The primary results are that at moderate redshifts ($0.05 < z < 0.8$) most galaxies are surrounded by extended gaseous envelopes of $\approx 160 \ h^{-1}$ kpc radius and many or most Ly$\alpha$ absorption systems arise in galaxies. The dependence of the incidence and extent of these gaseous envelopes on galaxy type and environment is discussed, and the application of galaxy and absorption system pairs to measurements of galaxy dynamics on large spatial scales and to significant redshifts is described.