Low-Redshift Damped Ly(alpha) Galaxies Toward the Quasars B2 0827+243, PKS 0952+179, PKS 1127-145, and PKS 1629+120

We present optical and near-infrared ground-based imaging results on four low-redshift damped Ly-alpha (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, PKS 0952+179, PKS 1127 145, and PKS 1629+120. 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. 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 smalller or approx. Z smaller or approx. 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 approx. 0.5.
Prepared in collaboration with the Naval Research Laboratory, Washington,DC; the Department of Astronomy, Ohio State University, Columbus,OH; and the Institut d' Astrophysique de Paris, Paris, France. Published in The Astrophysical Journal, v595, p94-108, Sep 2003.