Continuum and Emission-Line Properties of Broad Absorption Line Quasars

Abstract

We investigate the continuum and emission-line properties of 224 broad absorption line quasars (BALQSOs) with 0.9 ≲ z ≲ 4.4 drawn from the Sloan Digital Sky Survey Early Data Release, which contains 3814 bona fide quasars. We find that low-ionization BALQSOs (LoBALs) are significantly reddened as compared with normal quasars, in agreement with previous work. High-ionization BALQSOs (HiBALs) are also more reddened than the average non-BALQSO. Assuming SMC-like dust reddening at the quasar redshift, the amount of reddening needed to explain HiBALs is E ( B - V ) ∼ 0.023 and LoBALs is E ( B - V ) ∼ 0.077 (compared with the ensemble average of the entire quasar sample). We find that there are differences in the emission-line properties between the average HiBAL, LoBAL, and non-BAL quasar. These differences, along with differences in the absorption-line troughs, may be related to intrinsic quasar properties such as the slope of the intrinsic (unreddened) continuum; more extreme absorption properties are correlated with bluer intrinsic continua. Despite the differences among BALQSO subtypes and non-BALQSOs, BALQSOs appear to be drawn from the same parent population as non-BALQSOs when both are selected by their UV/optical properties. We find that the overall fraction of traditionally defined BALQSOs, after correcting for color-dependent selection effects due to different SEDs of BALQSOs and non-BALQSOs, is 13.4% ± 1.2% and shows no significant redshift dependence for 1.7 ≤ z ≤ 3.45. After a rough completeness correction for the effects of dust extinction, we find that approximately one in every six quasars is a BALQSO.