A Simple Disk Wind Model for Broad Absorption Line Quasars
  Approximately 20% of quasi-stellar objects (QSOs) exhibit broad, blue-shifted
absorption lines in their ultraviolet spectra. Such features provide clear
evidence for significant outflows from these systems, most likely in the form
of accretion disk winds. These winds may represent the "quasar" mode of
feedback that is often invoked in galaxy formation/evolution models, and they
are also key to unification scenarios for active galactic nuclei (AGN) and
QSOs. To test these ideas, we construct a simple benchmark model of an
equatorial, biconical accretion disk wind in a QSO and use a Monte Carlo
ionization/radiative transfer code to calculate the ultraviolet spectra as a
function of viewing angle. We find that for plausible outflow parameters,
sightlines looking directly into the wind cone do produce broad, blue-shifted
absorption features in the transitions typically seen in broad absorption line
QSOs. However, our benchmark model is intrinsically X-ray weak in order to
prevent overionization of the outflow, and the wind does not yet produce
collisionally excited line emission at the level observed in non-BAL QSOs. As a
first step towards addressing these shortcomings, we discuss the sensitivity of
our results to changes in the assumed X-ray luminosity and mass-loss rate,
Mdot(wind). In the context of our adopted geometry, Mdot(wind) ~ Mdot(acc) is
required in order to produce significant BAL features. The kinetic luminosity
and momentum carried by such outflows would be sufficient to provide
significant feedback.
