The Intrinsic Fraction of Broad Absorption Line Quasars

摘要: We carefully reconsider the problem of classifying broad-absorption line quasars (BALQSOs) and derive a new, unbiased estimate intrinsic BALQSO fraction from Sloan Digital Sky Survey (SDSS) DR3 quasi-stellar object (QSO) catalogue. first show that distribution objects selected by so-called 'absorption index' (AI) is clearly bimodal in log AI, with only one mode corresponding to definite BALQSOs. The surprisingly high fractions have recently been inferred AI-based samples are therefore likely be overestimated. then present two new approaches classification designed more robust than but also complete traditional 'balnicity (BI). Both yield observed around 13.5 per cent, while conservative third approach suggests an upper limit 18.3 cent. Finally, we discuss selection biases affect our fraction. After correcting for these biases, arrive at final This fBALQSO= 0.17 ± 0.01 (stat) 0.03 (sys) fBALQSO? 0.23 . conclude pointing out bimodality AI may evidence BAL-forming region has delineated physical boundaries.