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 similar to 1150-1470 angstrom with the Cosmic Origins Spectrograph on board the Hubble Space Telescope. This spectrum is highly peculiar, highlighted by the presence of faint (less than or similar to 2% of predictions based on H alpha), broad (greater than or similar to 10,000 km s(-1) at the base), and highly blueshifted (centroid at similar to -3500 km s(-1)) Ly alpha emission. The FUV continuum emission is slightly declining at shorter wavelengths (consistent with F-lambda proportional to 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) similar to 7 mag) broad absorption line region. Two possible geometric models are discussed in the context of these new results.