Massive molecular outflows and negative feedback in ULIRGs observed by
  Herschel-PACS
  Mass outflows driven by stars and active galactic nuclei are a key element in
many current models of galaxy evolution. They may produce the observed black
hole-galaxy mass relation and regulate and quench both star formation in the
host galaxy and black hole accretion. However, observational evidence of such
feedback processes through outflows of the bulk of the star forming molecular
gas is still scarce. Here we report the detection of massive molecular
outflows, traced by the hydroxyl molecule (OH), in far-infrared spectra of
ULIRGs obtained with Herschel-PACS as part of the SHINING key project. In some
of these objects the (terminal) outflow velocities exceed 1000 km/s, and their
outflow rates (up to ~1200 M_sol/yr) are several times larger than their star
formation rates. We compare the outflow signatures in different types of ULIRGs
and in starburst galaxies to address the issue of the energy source (AGN or
starburst) of these outflows. We report preliminary evidence that ULIRGs with a
higher AGN luminosity (and higher AGN contribution to L_IR) have higher
terminal velocities and shorter gas depletion time scales. The outflows in the
observed ULIRGs are able to expel the cold gas reservoirs from the centres of
these objects within ~1E6-1E8 years.
