A Study of Lyα Quasar Absorbers in the Nearby Universe

Spectroscopy of ten quasars obtained with the Goddard High ResolutionSpectrograph (GHRS) of the Hubble Space Telescope (HST) is presented. Aclustering analysis reveals an excess of nearest neighbor line pairs onvelocity scales of 250-750 km/s at a 95-98% confidence level. The hypothesisthat the absorbers are randomly distributed in velocity space can be ruled outat the 99.8% confidence level. No two-point correlation power is detected (xi <1 with 95% confidence). Lyman-alpha absorbers have correlation amplitudes onscales of 250-500 km/s at least 4-5 times smaller than the correlationamplitude of bright galaxies. A detailed comparison between absorbers in nearbygalaxies is carried out on a limited subset of 11 Lyman- alpha absorbers wherethe galaxy sample in a large contiguous volume is complete to M_B = -16.Absorbers lie preferentially in regions of intermediate galaxy density but itis often not possible to uniquely assign a galaxy counterpart to an absorber.This sample provides no explicit support for the hypothesis that absorbers arepreferentially associated with the halos of luminous galaxies. We have made apreliminary comparison of the absorption line properties and environments withthe results of hydrodynamic simulations. The results suggest that theLyman-alpha absorbers represent diffuse or shocked gas in the IGM that tracesthe cosmic web of large scale structure. (abridged)Comment: 36 pages of text, 15 figures, 4 tables, 36 file