2381/28723
Conor Wildy
Conor
Wildy
Michael R. Goad
Michael R.
Goad
J. T. Allen
J. T.
Allen
Quasar broad absorption line variability measurements using reconstructions of unabsorbed spectra
University of Leicester
2014
Science & Technology
Physical Sciences
Astronomy & Astrophysics
ASTRONOMY & ASTROPHYSICS
galaxies: active
quasars: absorption lines
quasars: general
DIGITAL SKY SURVEY
ACTIVE GALACTIC NUCLEI
EARLY DATA RELEASE
EMISSION-LINE
MULTIYEAR TIMESCALES
STELLAR OBJECTS
SI IV
C IV
OUTFLOWS
CONTINUUM
2014-04-02 14:28:39
Journal contribution
https://figshare.le.ac.uk/articles/journal_contribution/Quasar_broad_absorption_line_variability_measurements_using_reconstructions_of_unabsorbed_spectra/10172198
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.