Fast Molecular Outflows in Luminous Galaxy Mergers: Evidence for Quasar
  Feedback from Herschel
  We report the results from a systematic search for molecular (OH-119 um)
outflows with Herschel-PACS in a sample of 43 nearby (z < 0.3) galaxy mergers,
mostly ultraluminous infrared galaxies (ULIRGs) and QSOs. We find that the
character of the OH feature (strength of the absorption relative to the
emission) correlates with that of the 9.7-um silicate feature, a measure of
obscuration in ULIRGs. Unambiguous evidence for molecular outflows, based on
the detection of OH absorption profiles with median velocities more blueshifted
than -50 km/sec, is seen in 26 (70%) of the 37 OH-detected targets, suggesting
a wide-angle (~145 degrees) outflow geometry. Conversely, unambiguous evidence
for molecular inflows, based on the detection of OH absorption profiles with
median velocities more redshifted than +50 km/sec, is seen in only 4 objects,
suggesting a planar or filamentary geometry for the inflowing gas. Terminal
outflow velocities of ~-1000 km/sec are measured in several objects, but median
outflow velocities are typically ~-200 km s^{-1}. While the outflow velocities
show no statistically significant dependence on the star formation rate, they
are distinctly more blueshifted among systems with large AGN fractions and
luminosities [log (L_AGN / L_sun) > 11.8 +/- 0.3]. The quasars in these systems
play a dominant role in driving the molecular outflows. In contrast, the most
AGN dominated systems, where OH is seen purely in emission, show relatively
modest OH line widths, despite their large AGN luminosities, perhaps indicating
that molecular outflows subside once the quasar has cleared a path through the
obscuring material.
