The gaseous extent of galaxies and the origin of Ly alpha absorption systems. V. Optical and near-infrared photometry of Ly alpha-absorbing galaxies at z < 1

We present results of a program to obtain and analyze HST WFPC2 images and ground-based images of galaxies identified in an imaging and spectroscopic survey of faint galaxies in fields of HST spectroscopic target QSOs. Consid ering a sample of physically correlated galaxy and absorber pairs with gala xy-absorber cross-correlation amplitude xi (ga)(v, rho) > 1 and with galaxy impact parameter rho < 200 h(-1) kpc, we confirm and improve the results p resented by Lanzetta et al. and Chen et al. that (1) extended gaseous envel opes are a common and generic feature of galaxies of a wide range of lumino sity and morphological type, (2) the extent of tenuous gas [N(H I) <greater than or similar to> 10(14) cm(-2)] around galaxies scales with galaxy B-ba nd luminosity as r proportional to L-B(0.39 +/- 0.09), and (3) galaxy inter actions do not play an important role in distributing tenuous gas around ga laxies in most cases. We further demonstrate that (4) the gaseous extent of galaxies scales with galaxy K-band luminosity as r proportional to L-K(0.2 8 +/- 0.08), and (5) tenuous gas around typical L-* galaxies is likely to b e distributed in spherical halos of radius approximate to 180 h(-1) kpc of covering factor of nearly unity. The sample consists of 34 galaxy and absor ber pairs and 13 galaxies that do not produce Ly alpha absorption lines to within sensitive upper limits. Redshifts of the galaxy and absorber pairs r ange from z = 0.0752 to 0.8920 with a median of z = 0.3567; impact paramete r separations of the galaxy and absorber pairs range from rho = 12.4 to 175 .2 h(-1) kpc with a median of rho = 62.2 h(-1) kpc. Of the galaxies, 15 (32 %) are of B-band luminosity L-B < 0.25 L-B, and six (13%) are of low surfac e brightness. The galaxy sample is therefore representative of the galaxy p opulation over a large fraction of the Hubble time. Because galaxies of all morphological types possess extended gaseous halos and because the extent of tenuous gas around galaxies scales with galaxy K-band luminosity, we arg ue that galaxy mass-rather than recent star formation activity-is likely to be the dominant factor that determines the extent of tenuous gas around ga laxies. Nevertheless, applying the scaling relationship between the extent of Ly<alpha>-absorbing gas around galaxies and galaxy B-band luminosity, th e results of our analysis also suggest that the number density evolution of Ly alpha absorption systems may serve to constrain the evolution of the co moving galaxy B-band luminosity density (at least for the redshift interval between z similar to 0 and z similar to1 that has been studied in our surv ey).