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Low-ionization (MgII, FeII, FeIII) broad absorption line quasars (LoBALs)probe a relatively obscured quasar population, and could be at an earlyevolutionary stage for quasars. We study the intrinsic fractions of LoBALsusing the SDSS, 2MASS, and FIRST surveys. We find that the LoBAL fractions ofthe near infra-red (NIR) and radio samples are approximately 5--7 times higherthan those measured in the optical sample. This suggests that the fractionsmeasured in the NIR and radio bands are closer to the intrinsic fractions ofthe populations, and that the optical fractions are significantly biased due toobscuration effects, similar to high-ionization broad absorption line quasars(HiBALs). We also find that the LoBAL fractions decrease with increasing radioluminosities, again, similar to HiBALs. In addition, we find tentative evidencefor high fractions of LoBALs at high NIR luminosities, especially for FeLoBALswith a fraction of ~18 per cent at M_K_s < -31 mag. This population of NIRluminous LoBALs may be at an early evolutionary stage of quasar evolution. Weuse a two-component model of LoBALs including a pure geometric component and aluminosity dependent component at high NIR luminosities, and obtain better fitsthan those from a pure geometric model. Therefore, the LoBAL population can bemodelled as a hybrid of both the geometric and evolutionary models, where thegeometric component constitutes 3.4\pm0.3, 5.8\pm0.4, and 1.5\pm0.3 per cent ofthe quasar population for BI-LoBALs, AI-LoBALs, and FeLoBALs, respectively.Considering a population of obscured quasars that do not enter the SDSS survey,which could have a much higher LoBAL fraction, we expect that intrinsicfraction of LoBALs could be even higher.

The Intrinsic Fractions and Radio Properties of Low Ionization Broad Absorption Line Quasars