Blair D. Savage — Page 5

arXiv1997

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

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.

astro-ph↗

arXiv1995

The HST Quasar Absorption Line Key Project VII. Absorption Systems at $z_{\rm abs} \leq 1.3$

We present evidence that clumps of \lya lines are physically associated with about half of the extensive metal-line systems (absorption systems with four or more observed metal-line species) found in this paper, demonstrate that all four \lylimit systems discussed here correspond to extensive metal-line absorption systems, and present an extraordinary pair of extensive metal-line absorption systems within 2000~km/s of each other at $z~=~0.95$ that are probably an early manifestation of large scale structure. These results are obtained using ultraviolet spectra, taken with the higher-resolution gratings of the Faint Object Spectrograph of the Hubble Space Telescope, for four quasars with emission-line redshifts between 1.0 and 1.3. We also determine the evolution of \lya absorption lines at redshifts less than 1.3 by combining the results for 13 smaller redshift quasars discussed in Paper I of this series with the 4 moderate redshift quasars analyzed in the present paper. For $z_{\rm abs}~\leq~1.3$, the density of \lya lines with equivalent widths greater than 0.24~Å is adequately fit by $\left(dN/dz\right) =\left(dN/dz\right)_0 \cdot(1 + z)^γ$ with $(dN/dz)_0 = 24.3 \pm 6.6$ \lya lines per unit redshift, and $γ= 0.58 \pm 0.50$ (1-$σ$ uncertainties). This rate of evolution at low redshifts is less than the evolutionary rate inferred from several different ground-based data samples that pertain to high redshifts. The observed gaseous structures at redshifts of $0.5$ to $1.0$ with velocity dispersions of $6 \times 10^2$ \kms to $1.4 \times 10^3$ \kms (or velocity spans of $1.2 \times 10^3$ \kms to $3 \times 10^3$ \kms) constitute a constraint on cosmological models of structure formation.

astro-ph↗