Quasars with PV broad absorption in BOSS data release 9
  Broad absorption lines (BALs) found in a significant fraction of quasar
spectra identify high-velocity outflows that might be present in all quasars
and could be a major factor in feedback to galaxy evolution. Understanding the
nature of these flows requires further constraints on their physical
properties, including their column densities, for which well-studied BALs, such
as CIV 1548,1551, typically provide only a lower limit because of saturation
effects. Low-abundance lines, such as PV 1118,1128, indicate large column
densities, implying outflows more powerful than measurements of CIV alone would
indicate. We search through a sample of 2694 BAL quasars from the SDSS-III/BOSS
DR9 quasar catalog for such absorption, and we identify 81 `definite' and 86
`probable' detections of PV broad absorption, yielding a firm lower limit of
3.0-6.2% for the incidence of such absorption among BAL quasars. The
PV-detected quasars tend to have stronger CIV and SiIV absorption, as well as a
higher incidence of LoBAL absorption, than the overall BAL quasar population.
Many of the PV-detected quasars have CIV troughs that do not reach zero
intensity (at velocities where PV is detected), confirming that the outflow gas
only partially covers the UV continuum source. PV appears significantly in a
composite spectrum of non-PV-detected BAL quasars, indicating that PV
absorption (and large column densities) are much more common than indicated by
our search results. Our sample of PV detections significantly increases the
number of known PV detections, providing opportunities for follow-up studies to
better understand BAL outflow energetics.
