Broad Absorption Line Disappearance on Multi-year Timescales in a Large Quasar Sample
Abstract
We present 21 examples of C IV broad absorption line (BAL) trough disappearance in 19 quasars selected from systematic multi-epoch observations of 582 bright BAL quasars (1.9 < z < 4.5) by the Sloan Digital Sky Survey-I/II (SDSS-I/II) and SDSS-III. The observations span 1.1-3.9 yr rest-frame timescales, longer than have been sampled in many previous BAL variability studies. On these timescales, ≈2.3% of C IV BAL troughs disappear and ≈3.3% of BAL quasars show a disappearing trough. These observed frequencies suggest that many C IV BAL absorbers spend on average at most a century along our line of sight to their quasar. Ten of the 19 BAL quasars showing C IV BAL disappearance have apparently transformed from BAL to non-BAL quasars; these are the first reported examples of such transformations. The BAL troughs that disappear tend to be those with small-to-moderate equivalent widths, relatively shallow depths, and high outflow velocities. Other non-disappearing C IV BALs in those nine objects having multiple troughs tend to weaken when one of them disappears, indicating a connection between the disappearing and non-disappearing troughs, even for velocity separations as large as 10,000-15,000 km s-1. We discuss possible origins of this connection including disk-wind rotation and changes in shielding gas.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 2012
- DOI:
- 10.1088/0004-637X/757/2/114
- arXiv:
- arXiv:1208.0836
- Bibcode:
- 2012ApJ...757..114F
- Keywords:
-
- quasars: absorption lines;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- doi:10.1088/0004-637X/757/2/114