Quasar Broad Absorption Line Variability on Multiyear Timescales

• Published in: The Astrophysical journal Vol. 675; no. 2; pp. 985 - 1001
• Main Authors: Gibson, Robert R, Brandt, W. N, Schneider, Donald P, Gallagher, S. C
• Format: Journal Article
• Language: English
• Published: Chicago, IL IOP Publishing 10.03.2008; University of Chicago Press
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; Active galaxies; Quasars; Absorption line; galaxies: active; quasars: absorption lines; Variability; Galaxy nuclei; galaxies: nuclei; quasars: individual (LBQS 0010-0012, LBQS 0018+0047, LBQS 0021-0213, LBQS 0051-0019, LBQS 0055+0025, LBQS 0109-0128, LBQS 1208+1535, LBQS 1213+0922, LBQS 1234+0122, LBQS 1235+1453, LBQS 1243+0121, LBQS 1314+0116, LBQS 1331-0108)
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/527462

We use quantitative metrics to characterize the variation of C iv [lambda]1549 broad absorption lines (BALs) over 3-6 (rest-frame) years in a sample of 13 quasars at [image] and compare the results to previous studies of BAL variability on shorter timescales. The strong BALs in our study change in complex ways over 3-6 yr. Variation occurs in discrete regions only a few thousand kilometers per second wide, and the distribution of the change in absorption equivalent width broadens over time. We constrain the typical C iv BAL lifetime to be at least a few decades. While we do not find evidence to support a scenario in which the variation is primarily driven by photoionization on multiyear timescales, there is some indication that the variation is produced by changes in outflow geometry. We do not observe significant changes in the BAL onset velocity, indicating that the absorber is either far from the source or is being continually replenished and is azimuthally symmetric. It is not possible in a human lifetime to expand the timescales in our study by more than a factor of a few using optical spectroscopy. However, the strong variation we have observed in some BALs indicates that future studies of large numbers of BAL QSOs will be valuable to constrain BAL lifetimes and the physics of variation.