Hydrogen and metal absorption lines in PKS 0405 - 123 from the halos of low redshift galaxies

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 〈z₁〉 =0.1669 and 〈z₂〉 =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 z₁. 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 z₁ 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.