Quasar emission lines as probes of orientation: implications for disc
  wind geometries and unification
  The incidence of broad absorption lines (BALs) in quasar samples is often
interpreted in the context of a geometric unification model consisting of an
accretion disc and an associated outflow. We use the the Sloan Digital Sky
Survey (SDSS) quasar sample to test this model by examining the equivalent
widths (EWs) of CIV 1550\AA, Mg II 2800\AA, [OIII] 5007\AA\ and C III] 1909\AA.
We find that the emission line EW distributions in BAL and non-BAL quasars are
remarkably similar -- a property that is inconsistent with scenarios in which a
BAL outflow rises equatorially from a geometrically thin, optically thick
accretion disc. We construct simple models to predict the distributions from
various geometries; these models confirm the above finding and disfavour
equatorial geometries. We show that obscuration, line anisotropy and general
relativistic effects on the disc continuum are unlikely to hide an EW
inclination dependence. We carefully examine the radio and polarisation
properties of BAL quasars. Both suggest that they are most likely viewed (on
average) from intermediate inclinations, between type 1 and type 2 AGN. We also
find that the low-ionization BAL quasars in our sample are not confined to one
region of `Eigenvector I' parameter space. Overall, our work leads to one of
the following conclusions, or some combination thereof: (i) the continuum does
not emit like a geometrically thin, optically thick disc; (ii) BAL quasars are
viewed from similar angles to non-BAL quasars, i.e. low inclinations; (iii)
geometric unification does not explain the fraction of BALs in quasar samples.
