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 alpha, C IV lambda1549, and probably Mg II lambda2798 resonance lines are detected in an absorption system at z = 0.1670. An absorption system consisting of only Ly alpha 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.