Near-infrared spectroscopy of Arp interacting galaxies

We discuss near-infrared spectra of 20 interacting galaxies from the Arp Ca talog and analyze the properties of similar galaxies for which only optical spectra are available. We find excellent agreement between the types of ac tivity determined from the infrared and optical, demonstrating that obscura tion does not seriously bias the optical results. None of the 20 galaxies s how infrared spectral characteristics that differ from expectations for iso lated galaxies; the very strong shock-excited lines seen in a few interacti ng systems must be uncommon. Most of the galaxies in our infrared sample ar e the sites of starbursts that appear to have had durations of 1 to 5 Myr a nd 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 li kely to arise from shocks due to supernovae in late phase starbursts. In th e 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.