Probing High-Column Outflows in BALQSOs Using Metastable Helium

TL;DR

This paper demonstrates that metastable helium lines are effective probes of high column densities in BALQSOs, providing new insights into outflow properties through ground-based optical and infrared observations.

Contribution

It introduces the use of metastable helium triplet lines as a novel method for measuring high column densities in BALQSOs, complementing existing probes like PV.

Findings

Discovery of the first HeI*10830 BALQSO FBQS J1151+3822

Constraints on column density from optical and IR HeI* lines

Cloudy modeling suggests column density differences between LoBALs and FeLoBALs

Abstract

Outflows are believed to be ubiquitous and fundamentally important in active galaxies. Despite their importance, key physical properties of outflows remain poorly unconstrained; this severely limits study of the acceleration process. It is especially difficult to constrain the column density since most of the lines are saturated. However, column densities can be measured using ions that are expected to be relatively rare in the gas, since they are least likely to be saturated. Phosphorus, specifically the PV doublet at 1118 and 1128A, is generally regarded as a useful probe of high column densities because of its low abundance. We have found that the metastable neutral helium triplet is an equally valuable probe of high column densities in BALQSOs. The significant advantage is that it can be observed in the infrared (HeI*10830) and the optical (HeI*3889) bands from the ground in low-redshift (z<1.2) objects. We report the discovery of the first HeI*10830 BALQSO FBQS J1151+3822, and discuss constraints on the column density obtained from the optical and IR HeI* lines. In addition, a new observation revealing MgII and FeII absorption provides further constraints, and Cloudy modeling of HeI*, MgII, and FeII suggests that the difference between LoBALs and FeLoBALs is column density along the line of sight.