Evidence that 50% of BALQSO Outflows Are Situated at Least 100 pc from the Central Source

TL;DR

This study uses ionic excited state troughs to measure quasar outflow distances, revealing that at least half are located over 100 parsecs from the central source, impacting theories of outflow origins and galaxy influence.

Contribution

It provides the first large-scale evidence that a significant fraction of BAL quasar outflows are situated at least 100 parsecs away from the central black hole.

Findings

At least 50% of quasar outflows are beyond 100 parsecs from the center.

At least 12% of outflows are beyond 1000 parsecs.

Detection of S IV absorption is limited to 25% of C IV BAL outflows.

Abstract

The most robust way for determining the distance of quasar absorption outflows is the use of troughs from ionic excited states. The column density ratio between the excited and resonance states yields the outflow number density. Combined with a knowledge of the outflow's ionization parameter, a distance from the central source (R) can be determined. Here we report results from two surveys targeting outflows that show troughs from S IV. One survey includes 1091 SDSS and BOSS quasar spectra, and the other includes higher-quality spectra of 13 quasars observed with the Very Large Telescope. Our S IV samples include 38 broad absorption line (BAL) outflows, and four mini-BAL outflows. The S IV is formed in the same physical region of the outflow as the canonical outflow-identifying species C IV. Our results show that S IV absorption is only detected in 25% of C IV BAL outflows. The smaller detection fraction is due to the higher total column density ($N_H$) needed to detect S IV absorption. Since R empirically anticorrelates with $N_H$ the results of these surveys can be extrapolated to C IV quasar outflows with lower $N_H$ as well. We find that at least 50% of quasar outflows are at distances larger than 100 pc from the central source, and at least 12% are at distances larger than 1000 pc. These results have profound implications for the study of the origin and acceleration mechanism of quasar outflows and their effects on the host galaxy.