The nature and origin of z(a)approximate to z(e) absorption lines in the redshift 0.20 quasar, PKS 2135-147

We use new UV and optical spectra and an archival Hubble Space Telescope Wide Field Planetary Camera 2 (HST-WFPC2) image to study the z(a) approximate to z(e) absorber in the z(e) approximate to 0.20 QSO PKS 2135-147. The UV spectra, obtained with the Faint Object Spectrograph on HST, show strong z(a) approximate to z(e) absorption lines of C IV, N V, O VI, Ly alpha, and Ly beta. The z(a) approximate to z(e) line profiles are resolved, with deconvolved FWHM of 270-450 km s(-1). The Lyman decrement and the O VI and N V doublet ratios indicate that there are also narrower, optically thick line components, and there is evidence in the C IV and Ly alpha profiles for two blended components. Lower limits on the total column densities are of order 10(15) cm(-2) for all ions. The similar to 2:1 ratio of the C IV doublets suggests that the total C IV column density is near the lower limit. If the absorber is photoionized by the QSO and the derived relative columns in C IV and H I are roughly correct, then the metallicity must be at least solar. The location of the z(a) approximate to z(e) absorber remains uncertain. The line redshifts indicate that the clouds have little radial motion (less than +/- 200 km s(-1)) with respect to the QSO. This small velocity shift could mean that the absorber is outside of the deep gravitational potential of the QSO and the host-galaxy nucleus. Two similar to L-* galaxies in a small cluster centered on PKS 2135-147 lie within 36 h(-1) kpc projected distance and have redshifts consistent with causing or contributing to the z(a) approximate to z(e) lines. The extensive halo of the QSO's host galaxy could also contribute. Calculations show that the QSO is bright enough to photoionize gas up to O VI in the low-density halos of the host and nearby cluster galaxies. Nonetheless, there is indirect evidence for absorption much nearer the QSO, namely (1) the derived high (albeit uncertain) metallicity; (2) the relatively strong N v-absorption lines, which might be caused by a higher nitrogen abundance in the metal-rich gas; and (3) strong, lobe-dominated, steep-spectrum radio emission, which is known to correlate with a much higher incidence of(probably intrinsic) z(a) approximate to z(e) lines. We propose that the C IV/N V/O VI line ratios can be used as a general diagnostic of intrinsic versus intervening absorption, as long as the line saturation effects are understood.