QSO Absorbing Galaxies at z<~1: Deep Imaging and Spectroscopy in the Field of 3C 336

Abstract

We present very deep WFPC2 images and FOS spectroscopy from the Hubble Space Telescope (HST) together with numerous supporting ground-based observations of the field of the quasar 3C 336 ($z_{em}=0.927$). The observations are designed to investigate the nature of galaxies producing metal line absorption systems in the spectrum of the QSO. Along a single line of sight, we find at least 6 metal line absorption systems (of which 3 are newly discovered) ranging in redshift from 0.317 to 0.892. Through an extensive program of optical and IR imaging, QSO spectroscopy, and faint galaxy spectroscopy, we have identified 5 of the 6 metal line absorption systems with luminous (L_K > 0.1 L*_K) galaxies. These have morphologies ranging from very late-type spiral to S0, and exhibit a wide range of inclination and position angles with respect to the QSO sightline. The only unidentified absorber, despite our intensive search, is a damped Lyman $α$ system at $z_{abs}=0.656$. Analysis of the absorption spectrum suggests that the metal abundances ([Fe/H]$=-1.2$) in this system are similar to those in damped systems at $z \sim 2$, and to the two other damped systems for which abundances have been determined at $z <1$. We have found no examples of intrinsically faint galaxies ($L < 0.1 L^{\ast}$) at small impact parameters that might have been missed as absorber candidates in our previous ground-based imaging and spectroscopic programs on MgII absorbing galaxies. There are no bright galaxies (L > 0.1 L_K) within 50h^{-1} kpc which do not produce detectable metal lines (of Mg II 2796, 2803 and/or C IV 1548, 1550) in the QSO spectrum. All of these results generally support the inferences which we have previously reached from a larger survey for absorption-selected galaxies at $z\simlt 1$.