The Gaseous Extent of Galaxies and the Origin of Lyα Absorption Systems. V. Optical and Near‐Infrared Photometry of Lyα‐absorbing Galaxies at z < 1

Abstract

We present results of a program to obtain and analyze HST WFPC2 images and ground-based images of galaxies identiÐed in an imaging and spectroscopic survey of faint galaxies in Ðelds of HST spectroscopic target QSOs. Considering a sample of physically correlated galaxy and absorber pairs with galaxy-absorber cross-correlation amplitude and with galaxy impact parameter o \ 200 h~1 m ga (v, o) [ 1 kpc, we conÐrm and improve the results presented by Lanzetta et al. and Chen et al. that (1) extended gaseous envelopes are a common and generic feature of galaxies of a wide range of luminosity and morphological type, (2) the extent of tenuous gas [N(H cm~2] around galaxies scales with galaxy I) Z 1014 B-band luminosity as and (3) galaxy interactions do not play an important role in dis-r P L B 0.39B0.09, tributing tenuous gas around galaxies in most cases. We further demonstrate that (4) the gaseous extent of galaxies scales with galaxy K-band luminosity as and (5) tenuous gas around typical r P L K 0.28B0.08, galaxies is likely to be distributed in spherical halos of radius B180 h~1 kpc of covering factor of L * nearly unity. The sample consists of 34 galaxy and absorber pairs and 13 galaxies that do not produce Lya absorption lines to within sensitive upper limits. Redshifts of the galaxy and absorber pairs range from z \ 0.0752 to 0.8920 with a median of z \ 0.3567 ; impact parameter separations of the galaxy and absorber pairs range from o \ 12.4 to 175.2 h~1 kpc with a median of o \ 62.2 h~1 kpc. Of the galaxies, 15 (32%) are of B-band luminosity and six (13%) are of low surface brightness. The galaxy L B \ 0.25 L Bp sample is therefore representative of the galaxy population 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 argue that galaxy massÈrather than recent star formation activityÈis likely to be the dominant factor that determines the extent of tenuous gas around galaxies. Nevertheless, applying the scaling relationship between the extent of Lya-absorbing gas around galaxies and galaxy B-band luminosity, the results of our analysis also suggest that the number density evolution of Lya absorption systems may serve to constrain the evolution of the comoving galaxy B-band luminosity density (at least for the redshift interval between z D 0 and z D 1 that has been studied in our survey).