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Quasar broad absorption line variability measurements using reconstructions of unabsorbed spectra

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journal contribution
posted on 02.04.2014, 14:28 by Conor Wildy, Michael R. Goad, J. T. Allen
We present a two-epoch Sloan Digital Sky Survey and Gemini/GMOS+William Herschel Telescope/ISIS variability study of 50 broad absorption line (BAL) quasars of redshift range 1.9 < z<4.2, containing 38 Si IV and 59 C IV BALs and spanning rest-frame time intervals of ≈10 months to 3.7 years. We find that 35/50 quasars exhibit one or more variable BALs, with 58 per cent of Si IV and 46 per cent of C IVBALs showing variability across the entire sample. On average, Si IV BALs show larger fractional change in BAL pseudo-equivalent width than C IV BALs, as referenced to an unabsorbed continuum+emission line spectrum constructed using non-negative matrix factorization. No correlation is found between BAL variability and quasar luminosity, suggesting that ionizing continuum changes do not play a significant role in BAL variability (assuming the gas is in photoionization equilibrium with the ionizing continuum). A subset of 14 quasars have one variable BAL from each of Si IV and C IV with significant overlap in velocity space and for which variations are in the same sense (strengthening or weakening) and which appear to be correlated (98 per cent confidence). We find examples of both appearing and disappearing BALs in weaker/shallower lines with disappearance rates of 2.3 per cent for C IV and 5.3 per cent for Si IV, suggesting average lifetimes of 142 and 43 years, respectively. We identify five objects in which the BAL is coincident with the broad emission line, but appears to cover only the continuum source. Assuming a clumpy inhomogeneous absorber model and a typical size for the continuum source, we infer a maximum cloud radius of 10 [superscript 13] to 10 [superscript 14] cm, assuming Eddington limited accretion.

Funding

Science and Technology Facilities Council (STFC)

History

Citation

Monthly Notices of the Royal Astronomical Society, 2014, 437 (2), pp. 1976-1995

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy

Version

VoR (Version of Record)

Published in

Monthly Notices of the Royal Astronomical Society

Publisher

Oxford University Press on behalf of the Royal Astronomical Society

issn

0035-8711

eissn

1365-2966

Copyright date

2013

Available date

02/04/2014

Publisher version

http://mnras.oxfordjournals.org/content/437/2/1976

Language

en