LINER-like Extended Nebulae in ULIRGs: Shocks Generated by Merger Induced Flows

In this work we studied the two-dimensional ionization structure of the circumnuclear and extranuclear regions in a sample of six low−z Ultraluminous Infrared Galaxies using Integral Field Spectroscopy. The ionization conditions in the extranuclear regions of these galaxies (∼ 5−15 kpc) are typical of LINERs as obtained from the Veilleux-Osterbrock line ratio diagnostic diagrams. The range of observed line ratios is best explained by the presence of fast shocks with velocities of 150 to 500 km s, while the ionization by an AGN or nuclear starburst is Now in Astrophysikalisches Institut Potsdam, An der Sternwarte, 16, D 14482 Potsdam On leave from the Instituto de Astrof́ısica de Canarias (CSIC) Affiliated with the Space Telescope Division of the European Space Agency, ESTEC, Nordwijk, Netherlands