Constraining FeLoBAL outflows from absorption line variability

Iron low-ionization broad absorption lines (FeLoBALs) trace a rare class of quasar outflows with large column densities and potentially large kinetic energies that might be important for 'feedback' to galaxy evolution. In order to probe the physical properties of these outflows, we conducted a multiple-epoch, absorption line variability study of 12 FeLoBAL quasars spanning a redshift range of 0.7 <= z <= 1.9 over rest-frame time-scales of similar to 10 d to 7.6 yr. We detect absorption line variability with >= 8 sigma confidence in 3 out of the 12 sources in our sample over time-scales of similar to 0.6 to 7.6 yr. Variable wavelength intervals are associated with ground-and excited-state Fe II multiplets, the Mg II lambda lambda 2796, 2803 doublet, Mg I lambda 2852, and excited-state Ni II multiplets. The observed variability along with evidence of saturation in the absorption lines favours transverse motions of gas across the line of sight as the preferred scenario, and allows us to constrain the outflow distance from the supermassive black hole to be less than or similar to 69, 7, and 60 pc for our three variable sources. In combination with other studies, these results suggest that the outflowing gas in FeLoBAL quasars resides on a range of scales and includes matter within tens of parsecs of the central source.