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We present an optical spectroscopic study of a 90% complete sample of 17nearby ULIRGs with optical Seyfert nuclei, with the aim of investigating thenature of the nuclear warm gas outflows. A high proportion (94%) of our sampleshow disturbed emission line kinematics in the form of broad (FWHM > 500 kms-1) and/or strongly blueshifted (\Delta V < -150 km s-1) emission linecomponents. This proportion is significantly higher than found in a comparisonsample of non-Sy ULIRGs (19%). We also find evidence that the [OII]5007,4959emission lines in Sy-ULIRGs are broader and more asymmetric that in samples ofnon-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 emissionlines with a kinematic model derived from the strong [OIII]4959,5007 lines,using between 2 and 5 Gaussian components. From these fits we derive diagnosticline ratios that are used to investigate the ionization mechanisms for thedifferent kinematic components. We show that, in general, the line ratios areconsistent with gas of super-solar abundance photoionized by a combination ofAGN and starburst activity, with an increasing contribution from the AGN withincreasing FWHM of the individual kinematic components, and the AGNcontribution dominating for the broadest components. However, shock ionizationcannot be ruled out in some cases. Our derived upper limits on the massoutflows rates and kinetic powers of the emission line outflows show that theycan be as energetically significant as the neutral and molecular outflows inULIRGs-consistent with the requirements of the hydrodynamic simulations thatinclude AGN feedback. However, the uncertainties are large, and more accurateestimates of the radii, densities and reddening of the outflows are required toput these results on a firmer footing.

The importance of warm, AGN-driven outflows in the nuclear regions of nearby ULIRGs