The Intrinsic Fraction of Broad Absorption Line Quasars
By C. Knigge, S. Scaringi, M. Goad, Christopher E. Cottis University of Southampton, U. Leicester. 2008
139 citations recorded by the source corpus.
We carefully reconsider the problem of classifying broad-absorption line quasars (BALQSOs) and derive a new, unbiased estimate of the intrinsic BALQSO fraction from the Sloan Digital Sky Survey (SDSS) DR3 quasi-stellar object (QSO) catalogue. We first show that the distribution of objects selected by the so-called 'absorption index' (AI) is clearly bimodal in log AI, with only one mode corresponding to definite BALQSOs. The surprisingly high BALQSO fractions that have recently been inferred from AI-based samples are therefore likely to be overestimated. We then present two new approaches to the classification problem that are designed to be more robust than the AI, but also more complete than the traditional 'balnicity index' (BI). Both approaches yield observed BALQSO fractions around 13.5 per cent, while a conservative third approach suggests an upper limit of 18.3 per cent. Finally, we discuss the selection biases that affect our observed BALQSO fraction. After correcting for these biases, we arrive at our final estimate of the intrinsic BALQSO fraction. This is fBALQSO= 0.17 ± 0.01 (stat) ± 0.03 (sys) with an upper limit of fBALQSO? 0.23 . We conclude by pointing out that the bimodality of the log AI distribution may be evidence that the BAL-forming region has clearly delineated physical boundaries.
Subfields: Astronomy and Astrophysics, Instrumentation
View Paper: https://www.semanticscholar.org/paper/897be94b203f5e6e090b15e85d1ad3680f7d92cb
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Citations in the corpus
- A strong redshift dependence of the broad absorption line quasar fraction (2010, background): “…different probabilities of a BALQSO and non-BAL quasars entering the spectroscopic surveys used, the intrinsic fraction present in flux-limited optical surveys has been estimated as 22±4 (Hewett & Foltz 2003), 15.9±1.4 (Reichard et al. 2003b), 17±3 (Knigge et al. 2008), and 16.4±0.6 per cent (G09).”
- Quasar outflows and AGN feedback in the extreme UV: HST/COS observations of HE 0238−1904 (2013, background): “(Hewett & Foltz 2003; Ganguly & Brotherton 2008; Dai et al. 2008; Knigge et al. 2008; Dunn et al. 2012; Dai et al. 2012), and 5.”
- A CATALOG OF BROAD ABSORPTION LINE QUASARS IN SLOAN DIGITAL SKY SURVEY DATA RELEASE 5 (2008, background): “The observed fraction of BAL QSOs in optical surveys differs from the intrinsic fraction due to selection effects (e.g., Hewett et al. 1995; Krolik & Voit 1998; Reichard et al. 2003; Dai et al. 2008; Knigge et al. 2008).”