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Paper: Probing High-Column Outflows in BALQSOs Using Metastable Helium
Volume: 460, AGN Winds in Charleston
Page: 72
Authors: Leighly, K. M.; Lucy, A. B.; Dietrich, M.; Terndrup, D.; Gallagher, S. C.
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 P V doublet at 1118 and 1128Å, 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 (He I*λ 10830) and the optical (He I*λ 3888) bands from the ground in low-redshift (z < 1.2) objects. We report the discovery of the first He I*λ 10830 BALQSO FBQS J1151+3822, and discuss constraints on the column density obtained from the optical and IR He I* lines. In addition, a new observation revealing Mg II and Fe II absorption provides further constraints, and Cloudy modeling of He I*, Mg II and Fe II suggests that the difference between LoBALs and FeLoBALs is column density along the line of sight.
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