The NATURE OF DAMPED Lyα ABSORBING GALAXIES AT z ≤ 1–A PHOTOMETRIC REDSHIFT SURVEY OF DAMPED Lyα ABSORBERS

We study the nature of damped Lyα absorption (DLA) systems at z ≤ 1 using a sample of 11 DLA galaxies, for which accurate redshift measurements are available. Five of the 11 systems are identified in our on-going photometric redshift survey of DLA galaxies, while the remaining six systems are identified by previous groups using either spectroscopic or photometric redshift techniques. Absolute B-band magnitude of the galaxies range from MAB(B) = −15.3 to −20.3. Impact parameter separations of the galaxy and absorber pairs range from ρ = 0.31 to 25.4 h−1 kpc. We first demonstrate that the precision of photometric redshifts is sufficient for identifying DLA galaxies, because DLAs are rare and their intrinsically high column density implies a small impact parameter of the host galaxy to the QSO line of sight. We then adopt this first large DLA galaxy sample to study the neutral gas cross section of intermediate-redshift galaxies and examine the optical properties of DLA galaxies at z ≤ 1. The results of our study are: (1) the extent of neutral gas around intermediate-redshift galaxies scales with B-band luminosity as R/R∗ = [LB/LB∗ ] β with R∗ = 24 − 30 h −1 kpc and β = 0.26 −0.06 at N(H I) = 10 20 cm−2; (2) the observed incidence of the DLAs versus the Bband luminosity of the DLA galaxies is consistent with models derived from adopting Based in part on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5–26555. Hubble Fellow