Testing Quasar Unification: Radiative Transfer in Clumpy Winds
  Various unification schemes interpret the complex phenomenology of quasars
and luminous active galactic nuclei (AGN) in terms of a simple picture
involving a central black hole, an accretion disc and an associated outflow.
Here, we continue our tests of this paradigm by comparing quasar spectra to
synthetic spectra of biconical disc wind models, produced with our
state-of-the-art Monte Carlo radiative transfer code. Previously, we have shown
that we could produce synthetic spectra resembling those of observed broad
absorption line (BAL) quasars, but only if the X-ray luminosity was limited to
$10^{43}$ erg s$^{-1}$. Here, we introduce a simple treatment of clumping, and
find that a filling factor of $\sim0.01$ moderates the ionization state
sufficiently for BAL features to form in the rest-frame UV at more realistic
X-ray luminosities. Our fiducial model shows good agreement with AGN X-ray
properties and the wind produces strong line emission in, e.g., Ly \alpha\ and
CIV 1550\AA\ at low inclinations. At high inclinations, the spectra possess
prominent LoBAL features. Despite these successes, we cannot reproduce all
emission lines seen in quasar spectra with the correct equivalent-width ratios,
and we find an angular dependence of emission-line equivalent width despite the
similarities in the observed emission line properties of BAL and non-BAL
quasars. Overall, our work suggests that biconical winds can reproduce much of
the qualitative behaviour expected from a unified model, but we cannot yet
provide quantitative matches with quasar properties at all viewing angles.
Whether disc winds can successfully unify quasars is therefore still an open
question.
