BROAD ABSORPTION LINE DISAPPEARANCE ON MULTI-YEAR TIMESCALES IN A LARGE QUASAR SAMPLE

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 t...

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Bibliographic Details
Published in:The Astrophysical journal 2012-10, Vol.757 (2), p.114
Main Authors: Filiz Ak, N., Brandt, W. N., Hall, P. B., Schneider, D. P., Anderson, S. F., Gibson, R. R., Lundgren, B. F., Myers, A. D., Petitjean, P., Ross, Nicholas P., Shen, Yue, York, D. G., Bizyaev, D., Brinkmann, J., Malanushenko, E., Oravetz, D. J., Pan, K., Simmons, A. E., Weaver, B. A.
Format: Article
Language:English
Subjects:
ABSORPTION SPECTRA
ABSORPTION SPECTROSCOPY
ASTRONOMY
ASTROPHYSICS
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
CARBON IONS
QUASARS
ROTATION
Sciences of the Universe
STELLAR WINDS
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Summary: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.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/757/2/114