The z = 0.54 LoBAL Quasar SDSS J085053.12+445122.5. II. the Nature of Partial Covering in the Broad-absorption-line Outflow
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It has been known for 20 years that the absorbing gas in broad-absorption-line quasars does not completely cover the continuum emission region, and that partial covering must be accounted for to accurately measure the column density of the outflowing gas. However, the nature of partial covering itself is not understood. Extrapolation of the SimBAL spectral synthesis model of the Hubble Space Telescope Cosmic Origins Spectrograph UV spectrum from SDSS J0850+4451 reported by Leighly et al. to nonsimultaneous rest-frame optical and near-infrared spectra reveals evidence that the covering fraction has wavelength dependence and is a factor of 2.5 times higher in the UV than in the optical and near-infrared bands. The difference in covering fraction can be explained if the outflow consists of clumps that are small and either structured or clustered relative to the projected size of the UV continuum emission region and have a more diffuse distribution on size scales comparable to the size of the near-infrared continuum emission region. The lower covering fraction over the larger physical area results in a reduction of the measured total column density by a factor of 1.4-1.5 compared with the UV-only solution. This experiment demonstrates that we can compare rest-frame UV and near-infrared absorption lines, specifically He i∗λ10830, to place constraints on the uniformity of absorption gas in broad-absorption-line quasars.