Evidence for AGN Feedback in the Broad Absorption Lines and Reddening of
  Mrk 231
  We present the first J-band spectrum of Mrk 231, which reveals a large
\ion{He}{1}*$\lambda 10830$ broad absorption line with a profile similar to
that of the well-known \ion{Na}{1} broad absorption line. Combining this
spectrum with optical and UV spectra from the literature, we show that the
unusual reddening noted by \citet{veilleux13} is explained by a reddening curve
like those previously used to explain low values of total-to-selective
extinction in SNe Ia. The nuclear starburst may be the origin and location of
the dust. Spatially-resolved emission in the broad absorption line trough
suggests nearly full coverage of the continuum emission region. The broad
absorption lines reveal higher velocities in the \ion{He}{1}* lines (produced
in the quasar-photoionized \ion{H}{2} region) compared with the \ion{Na}{1} and
\ion{Ca}{2} lines (produced in the corresponding partially-ionized zone). {\it
Cloudy} simulations show that a density increase is required between the
\ion{H}{2} and partially-ionized zones to produce ionic column densities
consistent with the optical and IR absorption line measurements and limits, and
that the absorber lies $\sim 100\rm \, pc$ from the central engine. These
results suggest that the \ion{He}{1}* lines are produced in an ordinary quasar
BAL wind that impacts upon, compresses, and accelerates the nuclear starburst's
dusty effluent (feedback in action), and the \ion{Ca}{2} and \ion{Na}{1} lines
are produced in this dusty accelerated gas. This unusual circumstance explains
the rarity of \ion{Na}{1} absorption lines; without the compression along our
line of sight, Mrk~231 would appear as an ordinary FeLoBAL.
