The origins of a rich absorption line complex in a quasar at redshift 3.45

Abstract

We discuss the nature and origin of a rich complex of narrow absorption lines in the quasar J102325.31+514251.0 at redshift 3.447. We measure nine C iv(λλ1548, 1551) absorption line systems with velocities from −1400 to −6200 km s−1, and full widths at half-minimum ranging from 16 to 350 km s−1. We also detect other absorption lines in these systems, including H i, C iii, N v, O vi and Si iv. Lower ionization lines are not present, indicating a generally high degree of ionization in all nine systems. The total hydrogen column densities range from ≲ 1017.2 to 1019.1 cm−2. The tight grouping of these lines in the quasar spectrum suggests that most or all of the absorbing regions are physically related. We examine several diagnostics to estimate more directly the location and origin of each absorber. Four of the systems can be attributed to a quasar-driven outflow based on line profiles that are smooth and broad compared to thermal linewidths and to the typical absorption lines formed in intergalactic gas or galaxy haloes. Several systems also have other indicators of a quasar outflow origin, including partial covering of the quasar emission source (e.g. in systems with speeds too high for a starburst-driven flow), O vi column densities above 1015 cm−2 and an apparent line-lock in C iv (in two of the narrow profile systems). A search for line variability yielded null results, although with very poor constraints because the comparison spectra have much lower resolution. Altogether (but not including the tentative line-lock) there is direct evidence for six of the nine systems forming in a quasar outflow. Consistent with a near-quasar origin, eight of the systems have metallicity values or lower limits in the range Z≥ 1–8 Z⊙. The lowest velocity system, which has an ambiguous location based on the diagnostics mentioned above, also has the lowest metallicity, Z≤ 0.3 Z⊙, and might form in a non-outflow environment farther from the quasar. Overall, however, this complex of narrow absorption lines can be identified with a highly structured, multicomponent outflow from the quasar. The high metallicities are similar to those derived for other quasars at similar redshifts and luminosities, and are consistent with evolution scenarios wherein quasars appear after the main episodes of star formation and metal enrichment in the host galaxies.