High‐Resolution Spectra of Intrinsic Absorption Lines in the Quasi‐stellar Object UM 675

Abstract

We discuss high-resolution (~9 km s-1) Keck Observatory spectra of the associated (za ≈ ze) absorption lines in the ze = 2.15 QSO UM 675. In a previous paper we showed that the time-variable absorption lines require a minimum gas density of ~4000 cm-3 and a maximum distance of ~1 kpc from the QSO. We also inferred metallicities of Z Z☉ from an assortment of measured column densities. The new data yield absorption-line profiles for Lyα, and C IV, more reliable column densities, and evidence for partial coverage of the background emission source(s). The za ≈ ze line profiles are dominated by broad (FWHM ≈ 470 km s-1) and relatively smooth components with centroids shifted roughly -1500 km s-1 from the emission-line redshift. Much weaker narrow-line components (with FWHM ≈ 55 and 29 km s-1) are also detected inside the broad C IV and N V profiles, but they contribute negligibly to the total equivalent widths and column densities. The complex of broad and narrow lines indicates formation in an outflow, possibly in discrete ejection events, where distinct regions have the same outflow velocity but different (nonthermal) velocity dispersions. The doublet ratios in C IV indicate that its broad and narrow components both cover less than 50% of the emission source(s). This is further strong evidence for absorption near the QSO by clouds that are 0.1 pc across. In contrast, the Lyα absorber covers 83% of the emission source(s) and O VI covers 60%, indicating that different ions can have different coverage fractions. Scaling all of the metallic column densities upward by amounts appropriate for the C IV coverage fraction implies a metallicity of 2 Z☉. However, the metallicity could be much lower if large H I columns are hidden in the Lyα profile.