The Dependence of C IV Broad Absorption Line Properties on Accompanying Si IV and Al III Absorption: Relating Quasar-Wind Ionization Levels, Kinematics, and Column Densities

TL;DR

This study investigates how the properties of C IV broad absorption lines in quasars vary depending on the presence of lower ionization lines like Si IV and Al III, revealing correlations with ionization, kinematics, and column density.

Contribution

It provides a detailed observational analysis linking BAL properties to ionization levels and variability, enhancing understanding of quasar wind structures.

Findings

C IV BALs with lower ionization lines are deeper, broader, and less variable.

Lines without Si IV or Al III may be mildly saturated or unsaturated.

Correlations support accretion-disk wind models.

Abstract

We consider how the profile and multi-year variability properties of a large sample of C IV Broad Absorption Line (BAL) troughs change when BALs from Si IV and/or Al III are present at corresponding velocities, indicating that the line-of-sight intercepts at least some lower ionization gas. We derive a number of observational results for C IV BALs separated according to the presence or absence of accompanying lower ionization transitions, including measurements of composite profile shapes, equivalent width (EW), characteristic velocities, composite variation profiles, and EW variability. We also measure the correlations between EW and fractional-EW variability for C IV, Si IV, and Al III. Our measurements reveal the basic correlated changes between ionization level, kinematics, and column density expected in accretion-disk wind models; e.g., lines-of-sight including lower ionization material generally show deeper and broader C IV troughs that have smaller minimum velocities and that are less variable. Many C IV BALs with no accompanying Si IV or Al III BALs may have only mild or no saturation.