The Surprising Absence of Absorption in the Far-Ultraviolet Spectrum of
  Mrk 231
  Mrk 231, the nearest (z = 0.0422) quasar, hosts both a galactic-scale wind
and a nuclear-scale iron low-ionization broad absorption line (FeLoBAL)
outflow. We recently obtained a far-ultraviolet (FUV) spectrum of this object
covering ~1150 - 1470 A with the Cosmic Origins Spectrograph on board the
Hubble Space Telescope. This spectrum is highly peculiar, highlighted by the
presence of faint (~< 2% of predictions based on H-alpha), broad (>~ 10,000
km/s at the base), and highly blueshifted (centroid at ~ -3500 km/s) Ly-alpha
emission. The FUV continuum emission is slightly declining at shorter
wavelengths (consistent with F_lambda ~ lambda^1.7) and does not show the
presence of any obvious photospheric or wind stellar features. Surprisingly,
the FUV spectrum also does not show any unambiguous broad absorption features.
It thus appears to be dominated by the AGN, rather than hot stars, and
virtually unfiltered by the dusty FeLoBAL screen. The observed Ly-alpha
emission is best explained if it is produced in the outflowing BAL cloud
system, while the Balmer lines arise primarily from the standard broad emission
line region seen through the dusty (A_V ~ 7 mag.) broad absorption line region.
Two possible geometric models are discussed in the context of these new
results.
