Dependence of the BALQSO fraction on Radio Luminosity

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  • 28 January 2008
Abstract
We find that the fraction of Broad Absorption line quasars (BALQSOs) among the FIRST radio sources in the Sloan Data Release 3, is about 45.5^{+7.6}_{-7.5}% at the faintest radio powers detected (L_{1.4 GHz}~10^{32} erg/s), and rapidly drops to 23.9^{+3.4}_{-3.1}% at L_{1.4 GHz}~3*10^{33} erg/s. While the high fraction at low radio power is consistent with the recent near-IR estimate by Dai et al. (2007), the lower fraction at high radio powers is intriguing. The trend is independent of the redshift limits, the optical and radio flux selection limits, the exact definition of a BALQSO, or the exact definition of a radio match. The absorption index decreases with the radio luminosity while the mean maximum wind velocity is roughly a constant at all radio powers. We also find that at fixed optical magnitude, the highest bins of radio luminosity are preferentially populated by non-BALQSOs, consistent with the overall trend. These results are difficult to reconcile with a strictly evolutionary model for the BALQSO and radio emission phases, while a simple geometric model where the apparent radio luminosity function is partly due to beamed, non-BALQSOs can reproduce the results.

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