VLT/X-Shooter Survey of BAL Quasars: Large Distance Scale and AGN Feedback

TL;DR

This survey of BAL quasars using VLT/X-shooter reveals most outflows are located hundreds to thousands of parsecs from the AGN, with some capable of significant feedback, challenging previous assumptions about their proximity to the central source.

Contribution

First unbiased measurement of BAL outflow distances showing they are generally far from the AGN, with implications for feedback and galaxy evolution.

Findings

Most outflows are located at 100-4500 pc from the AGN.

At least two outflows have enough kinetic energy for significant feedback.

Outflows exhibit a wide range of velocities and ionization states.

Abstract

We conducted a survey of quasar outflows using the VLT/X-shooter spectrograph. When choosing the 14 BAL and mini-BALs comprising this sample, the data did not cover the S IV and S IV* troughs, whose ratio can be used to determine the distance of the outflows from the central source (R). Therefore, this "Blind Survey" is unbiased towards a particular distance scale. Out of the eight outflows where R can be measured, six have R > 100 pc (spanning the range 100-4500 pc), one has R > 10 pc, and only one (at R < 60 pc) is compatible with a much smaller R scale. At least two of the outflows have a kinetic luminosity greater than 0.5% of their Eddington luminosity, implying that they are able to provide significant AGN feedback. The outflows span a range of 0 to -10000 km s$^{-1}$ in velocity; total column density between 10$^{20}$ - 10$^{22.5}$ cm$^{-2}$ ; ionization parameter ($U_H$ ) in the range 0.01 - 1; and electron number density between 10$^3$ - 10$^{5.5}$ cm$^{-3}$ , with one upper and one lower limit. The results of this survey can be extrapolated to the majority of BAL outflows, implying that most of these outflows are situated far away from the AGN accretion disk; and that a significant portion of them can contribute to AGN feedback processes.