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

Abstract

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.