Physical Conditions of Five O VI Absorption Systems Towards PG $1522+101$

Abstract

We present the analysis of five O VI absorbers identified across a redshift path of z ∼ (0.6 − 1.3) towards the background quasar PG 1522 + 101 with information on five consecutive ionization stages of oxygen from O II to O VI. The combined HST and Keck spectra cover UV, redshifted EUV, and optical transitions from a multitude of ions spanning ionization energies in the range of ∼ (13 − 300) eV. Low ionization (C II, O II, Si II, Mg II) and very high ionization species (Ne VIII, Mg X) are non-detections in all the absorbers. Three of the absorbers have coverage of He I, in one of which it is a > 3σ detection. The kinematic structures of these absorbers are extracted from C IV detected in HI RE S spectra. The farthest absorber in our sample also contains the detections of Ne V and Ne VI. Assuming co-spatial absorbing components, the ionization models show the medium to be multiphased with smallscale density-temperature inhomogeneities that are sometimes kinematically unresolved. In two of the absorbers, there is an explicit indication of the presence of a warm gas phase (T 10 5 K) traced by O VI. In the remaining absorbers, the column densities of the ions are consistent with a non-uniform photoionized medium. The sub-solar [C/O] relative abundances inferred for the absorbers point at enrichment from massive Type II supernovae. Despite metal enrichment, the inferred wide range for [O/H] ∼ [−2.1, +0.2] amongst the absorbers along with their anti-correlation with the observed H I suggest poor small-scale mixing of metals with hydrogen in the regions surrounding galaxies and the IGM.