Low-Redshift Damped Lyα Galaxies toward the Quasars B2 0827+243, PKS 0952+179, PKS 1127-145, and PKS 1629+120

Abstract

We present optical and near-infrared ground-based imaging results on four low-redshift damped Lyα (DLA) galaxies. The corresponding DLA systems were discovered in our Hubble Space Telescope spectroscopic surveys for DLA lines in known strong Mg II absorption-line systems toward the quasars B2 0827+243 (z_DLA=0.525), PKS 0952+179 (z_DLA=0.239), PKS 1127-145 (z_DLA=0.313), and PKS 1629+120 (z_DLA=0.532). Two of the four DLA galaxies have confirmed slit redshifts, one has a photometric redshift consistent with the absorption-line redshift, and the fourth identification is based on the galaxy's proximity to the quasar sight line. The DLA galaxies span a mixture of morphological types from patchy, irregular, and low surface brightness to spiral galaxies. The luminosities range from 0.02L^*_K to 1.2L^*_K. We also discovered several extremely red objects (EROs) in two of these fields and discuss the possibility that they are associated with the DLA galaxies. These observations add to the small but growing list of DLA galaxies at low redshift. At the present time, 14 DLA galaxies in the redshift range 0.05<~z<~1 have been studied. The distributions of DLA galaxy properties for these 14 cases are discussed, and some important trends emerge. Low-luminosity dwarf galaxies with small impact parameters dominate this small sample. Also, four of the five highest column density systems, which dominate in the determination of the cosmological neutral gas mass density, arise in low surface brightness dwarf galaxies. Zwaan et al. have shown that only 15% of the neutral gas at the present epoch is contained in low surface brightness galaxies. Thus, if the low-redshift DLA galaxy trends hold up with larger samples, it would indicate that a different population of objects is responsible for the bulk of the neutral hydrogen gas in the universe at z~0.5.

Based on observations obtained with the 3.5 m WIYN Telescope on Kitt Peak, operated for the NSF by the Association of Universities for Research in Astronomy (AURA), Inc. (WIYN is a joint facility of University of Wisconsin, Indiana University, Yale University, and NOAO), the Infrared Telescope Facility, which is operated by the University of Hawaii under a cooperative agreement with the National Aeronautics and Space Administration, the Hiltner 2.4 m Telescope on Kitt Peak, operated by MDM Observatory (this is a joint facility of University of Michigan, Dartmouth College, Ohio State University, and Columbia University), and the 3.6 m European Southern Observatory New Technology Telescope on La Silla, Chile.