The Nature of Damped Lyα Absorbing Galaxies at z ≤ 1: A Photometric Redshift Survey of Damped Lyα Absorbers

  • Chen H
  • Lanzetta K
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We study the nature of damped Ly? absorption (DLA) systems at zusing a sample of 11 DLA galaxies, for which accurate redshift measurements
are available. Five of the 11 systems are identified in our ongoing
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 magnitudes of
the galaxies range from MAB(B)=-15.3 to -20.3. Impact parameter separations
of the galaxy and absorber pairs range from ?=0.31 to 25.4 h-1 kpc.
We first demonstrate that the precision of photometric redshifts
is sufficient for identifying DLA galaxies because DLA systems 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 zare as follows: (1) the extent of neutral gas around intermediate-redshift
galaxies scales with B-band luminosity as R/R*=(LB/LB*)? with R*=24-30
h-1 kpc and ?=0.26+0.24-0.06 at N(HI)=1020 cm-2 (2) the observed
incidence of the DLA systems versus the B-band luminosity of the
DLA galaxies is consistent with models derived from adopting a known
galaxy B-band luminosity function and the best-fit scaling relation
of the neutral gas cross section at MAB(B)-5loghof the observed and predicted number density of DLA systems supports
that luminous galaxies can explain most of the DLA systems found
in QSO absorption line surveys and a large contribution of dwarfs
(MAB(B)-5logh>=-17) to the total neutral gas cross section is not
necessary; (4) of the 11 DLA systems studied, 45% are disk dominated,
22% are bulge dominated, 11% are irregular, and 22% are in galaxy
groups, indicating that galaxies that give rise to the DLA systems
span a wide range of morphological types and arise in a variety of
galaxy environments; and (5) galaxies that contain the bulk of neutral
gas in the universe do not appear to exhibit a substantial luminosity
evolution between z=0 and 1.

Author-supplied keywords

  • low-z-DLAs SUNY

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  • Hsiao‐Wen Chen

  • Kenneth M. Lanzetta

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