The orientation and polarization of broad absorption line quasars
  We present new spectropolarimetric observations of 8 radio-loud broad
absorption line (BAL) quasars, and combine these new data with our previous
spectropolarimetric atlases (of both radio-loud and radio-quiet objects) in
order to investigate the polarization properties of BAL quasars as a group. The
total (radio-selected) sample includes 36 (26) high-ionization and 22 (15)
low-ionization BAL quasars. On average, we confirm that broad emission lines
are polarized at a level similar to or less than the continuum and broad
absorption troughs are more highly polarized, but we note that these properties
are not true for all individual objects. Of the whole sample, 18 (31%) have
high (>2%) continuum polarization, including 45% of the LoBALs and 22% of
HiBALs. We identify a few correlations between polarization and other quasar
properties, as well as some interesting non-correlations. In particular,
continuum polarization does not correlate with radio spectral index, which
suggests that the polarization is not due to a standard geometry and preferred
viewing angle to BAL quasars. The polarization also does not correlate with the
amount of intrinsic dust reddening, indicating that the polarization is not
solely due to direct light attenuation either. Polarization does appear to
depend on the minimum BAL outflow velocity, confirming the results of previous
studies, and it may correlate with the maximum outflow velocity. We also find
that continuum polarization anti-correlates with the polarization in the C IV
broad emission and broad absorption. These results suggest that the
polarization of BAL quasars cannot be described by one simple model, and that
the scatterer location and geometry can vary significantly from object to
object.
