Echelle Spectroscopy of QSO Absorption Line Systems with Metals in the Direction of HS 1700+6416

Abstract

We present a high signal-to-noise high resolution spectrum of the radio-quiet QSO HS1700+6416 (z = 2.72). Analysis of the absorption line systems with metals yields the following results. (1) The dense cluster of C IV doublets at 2.432 < z(abs) < 2.441 shows the weak line of one C IV absorber apparently aligned with the strong line of a different C IV doublet, i.e., line locked, for two pairs of C IV absorbers. This is surprising since these absorption lines are displaced by more than 24000 km/s from the QSO redshift, but it is possible that these alignments are coincidental. (2) Physical conditions in the Lyman limit absorber at z(abs) = 2.3150 differ significantly from the Galactic gaseous halo, and photoionization models require [Si/H] > -0.95 and [Al/H] > -0.96 for the strongest component of this absorber. Abundances of three other Lyman limit absorbers are also derived from photoionization models. (3) Unsaturated C IV and rather strong N V are detected in the associated absorber at z(abs) = 2.7125. The apparent column density profiles indicate that N V is affected by unresolved saturation or that the N V absorbing gas does not completely cover the QSO flux source. From photoionization models we derive [N/H] > -0.65 and [C/H] > -0.82. (4) We tentatively conclude that the number of Mg II systems detected per unit redshift is dominated by weak Mg II lines with rest equivalent width less than 0.3 A.