On the Fraction of Broad Absorption Line Quasi‐stellar Objects

Recent evidence indicates that some, if not all, broad absorption line quasi-stellar objects (BAL QSOs) may have significantly attenuated continuum compared with normal (non-BAL) radio-quiet QSOs. This attenuation has important implications for the fraction of radio-quiet QSOs that show the BAL QSO phenomenon, implying a fraction of at least 30%, much larger than the canonical value of 10%. This also implies a covering factor for the BAL region of ≥30%. Constraints can in turn be placed on how many of the BAL QSOs are in fact heavily attenuated, if we make the reasonable assumption that scattering within the BAL region produces the polarization.