Variation of Ionizing Continuum: The Main Driver of Broad Absorption Line Variability

Journal Article · Sat Apr 01 04:00:00 EDT 2017 · Astrophysical Journal, Supplement Series

DOI:https://doi.org/10.3847/1538-4365/AA647A· OSTI ID:22872833

He, Zhicheng; Wang, Tinggui; Zhou, Hongyan; Liu, Guilin; Yang, Chenwei; Dou, Liming; Sun, Luming ^[1]; Bian, Weihao ^[2]

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1. CAS Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei, Anhui 230026 (China)
2. Department of Physics and Institute of Theoretical Physics, Nanjing Normal University, Nanjing 210023 (China)

We present a statistical analysis of the variability of broad absorption lines (BALs) in quasars using the large multi-epoch spectroscopic data set of the Sloan Digital Sky Survey Data Release 12 (SDSS DR12). We divide the sample into two groups according to the pattern of the variation of C iv BAL with respect to that of a continuum: the equivalent widths (EW) of the BAL decreases (increases) when the continuum brightens (dims) as group T1; and the variation of the EW and the continuum in the opposite relation of group T2. We find that T2 has significantly (P{sub T}<10{sup −6}, Students T Test) higher EW ratios (R) of Si iv to C iv BAL than T1. Our result agrees with the prediction of photoionization models that C{sup +3} column density increases (decreases) if there is a (or no) C{sup +3} ionization front, while R decreases with the incident continuum. We show that BAL variabilities in at least 80% of quasars are driven by the variation of an ionizing continuum, while other models that predict uncorrelated BAL and continuum variability contribute less than 20%. Considering large uncertainty in the continuum flux calibration, the latter fraction may be much smaller. When the sample is binned into different time intervals between the two observations, we find significant difference in the distribution of R between T1 and T2 in all time-bins down to ΔT<6 days, suggesting that the BAL outflow in a fraction of quasars has a recombination timescale of only a few days.

• OSTI ID: 22872833
• Journal Information: Astrophysical Journal, Supplement Series, Journal Name: Astrophysical Journal, Supplement Series Journal Issue: 2 Vol. 229; ISSN 0067-0049; ISSN APJSA2
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION
CALIBRATION
CARBON IONS
DENSITY
GALAXIES
PHOTOIONIZATION
QUASARS
RECOMBINATION
SKY