Hydrogen and Metal Absorption Lines in PKS 0405-123 From the Halos of Low Redshift Galaxies

Abstract

Hubble Space Telescope ultraviolet spectra and ground-based optical spectra of the bright quasar PKS 0405 - 123 are used to identify two absorption-line systems probably produced by the halos of foreground galaxies. The quasar lies in a rich galaxy field. Loose groups of galaxies are present in the field at <z_1_> = 0.1669 and <z_2_> = 0.3519. Ly α, C IV λ1549, and probably Mg II λ2798 resonance lines are detected in an absorption system at z = 0.1670. An absorption system consisting of only Ly α is observed at z = 0.3516. We cannot be completely certain which foreground galaxy is responsible for the metal line absorption system at z_1_. A likely candidate is a large, luminous, early-type spiral 40" (projected distance 78h^-1^ kpc) to the east of the quasar. However, the origin of the z_1_ system could possibly be a small, undetected galaxy more precisely aligned along our line of sight to PKS 0405 - 123, or a very faint galaxy whose redshift has not yet been measured.