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It has been known for 20 years that the absorbing gas in broad absorptionline quasars does not completely cover the continuum emission region, and thatpartial covering must be accounted for to accurately measure the column densityof the outflowing gas. However, the nature of partial covering itself is notunderstood. Extrapolation of the SimBAL spectral synthesis model of the HST COSUV spectrum from SDSS J0850+4451 reported by Leighly et al. 2018 tonon-simultaneous rest-frame optical and near-infrared spectra reveals evidencethat the covering fraction has wavelength dependence, and is a factor of 2.5times higher in the UV than in the optical and near-infrared bands. Thedifference in covering fraction can be explained if the outflow consists ofclumps that are small and either structured or clustered relative to theprojected size of the UV continuum emission region, and have a more diffusedistribution on size scales comparable to the near-infrared continuum emissionregion size. The lower covering fraction over the larger physical area resultsin a reduction of the measured total column density by a factor of 1.6 comparedwith the UV-only solution. This experiment demonstrates that we can comparerest-frame UV and near-infrared absorption lines, specifically HeI*10830, toplace constraints on the uniformity of absorption gas in broad absorbing linequasars.

The z=0.54 LoBAL Quasar SDSS J085053.12+445122.5: II. The Nature of Partial Covering in the Broad-Absorption-Line Outflow