We discuss near-infrared spectra of 20 interacting galaxies from the Arp Catalog and analyze the properties of similar galaxies for which only optical spectra are available. We find excellent agreement between the types of activity determined from the infrared and optical, demonstrating that obscuration does not seriously bias the optical results. None of the 20 galaxies show infrared spectral characteristics that differ from expectations for isolated galaxies; the very strong shock-excited lines seen in a few interacting systems must be uncommon. Most of the galaxies in our infrared sample are the sites of starbursts that appear to have had durations of 1 to 5 Myr and to be observed 3 to 10 Myr after the peak star-forming episode. Four of the 20 galaxies have LINER or composite starburst/LINER spectra that are likely to arise from shocks due to supernovae in late phase starbursts. In the full interacting galaxy sample, there is a substantial excess of Seyfert 2 nuclei, supporting previous indications that this type of activity tends to occur in interacting host galaxies.

L.V. acknowledges support from the Agenzia Spaziale Italiana under grants 95-RS-120 and ARS-96-66. During the course of this work, A.A.-H. was supported by the National Aeronautics and Space Administrationon grant NAG5-3042 through the University of Arizona.The work of G.H.R. was supported under NSF grant AST 95-29190. This research made use of the NASA/IPAC Extragalactic Database(NED),which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract to the National Aeronautics and Space Administration.

Peer reviewed