The importance of warm, AGN-driven outflows in the nuclear regions of
  nearby ULIRGs
  We present an optical spectroscopic study of a 90% complete sample of 17
nearby ULIRGs with optical Seyfert nuclei, with the aim of investigating the
nature of the nuclear warm gas outflows. A high proportion (94%) of our sample
show disturbed emission line kinematics in the form of broad (FWHM > 500 km
s-1) and/or strongly blueshifted (\Delta V < -150 km s-1) emission line
components. This proportion is significantly higher than found in a comparison
sample of non-Sy ULIRGs (19%). We also find evidence that the [OII]5007,4959
emission lines in Sy-ULIRGs are broader and more asymmetric that in samples of
non-ULIRG Seyferts.
  The Sy-ULIRG sample encompasses a wide diversity of emission line profiles.
In most individual objects we are able to fit the profiles of all the emission
lines with a kinematic model derived from the strong [OIII]4959,5007 lines,
using between 2 and 5 Gaussian components. From these fits we derive diagnostic
line ratios that are used to investigate the ionization mechanisms for the
different kinematic components. We show that, in general, the line ratios are
consistent with gas of super-solar abundance photoionized by a combination of
AGN and starburst activity, with an increasing contribution from the AGN with
increasing FWHM of the individual kinematic components, and the AGN
contribution dominating for the broadest components. However, shock ionization
cannot be ruled out in some cases. Our derived upper limits on the mass
outflows rates and kinetic powers of the emission line outflows show that they
can be as energetically significant as the neutral and molecular outflows in
ULIRGs-consistent with the requirements of the hydrodynamic simulations that
include AGN feedback. However, the uncertainties are large, and more accurate
estimates of the radii, densities and reddening of the outflows are required to
put these results on a firmer footing.
