Tracing the outflow of a z = 0.334 FeLoBAL: New constraints from low-ionization absorbers in FBQS J1151+3822

We show for the first time that FBQS J1151+3822 is an iron low-ionization broad absorption line quasar (FeLoBAL QSO), the second-brightest and second-closest known example of this class. He I* and Fe II together act as an effective analytical tool, allowing us to obtain useful kinematic constraints from photoionization models of the outflow without needing to assume any particular acceleration model. The main outflow's log ionization parameter is –1.5, the log hydrogen density (cm^–3) 5.5-8, the log hydrogen column density (cm^–2) 21.7-21.9, the absorption radius 7.2-127 pc, and the kinetic luminosity is 0.16%-4.5% of the bolometric luminosity. We obtain line-of-sight covering fractions of ∼0.25 for strong Fe II, ∼0.5 for He I*, and ∼0.6 for Mg II. Narrower and shallower absorption lines from weaker Fe II and Mn II with an outflow velocity of ∼3400 km s^–1 have appeared between 2005 and 2011, suggesting that dense cores may have condensed inside the main outflow. Consideration of the literature might suggest that the FBQS J1151+3822 outflow is a member of a rare and distinct subclass of FeLoBALs with high densities and correspondingly small absorption radii. We find, however, that such outflows are not necessarily a distinct subclass, and that their apparent rarity could be a symptom of selection bias in studies using density-sensitive lines.