'Astronomical Society of the Pacific Conference Series'
Abstract
We discuss four interacting pairs of galaxies with emission from tidally stripped ionized gas. Three of the pairs (Kar 29, Arp 194, and ESO 253-IG026) host a collisional ring galaxy, and a head-on collision cannot be ruled out even in the fourth case (NGC 7592). Emitting regions are revealed outside the disk of the ring galaxies, either in the form of a bright filament or of blobs. Long-slit spectroscopic data reveal gas kinematics dominated by non-rotational motions. We are able to show that ionized gas in the vicinity (from a few kpc down to our resolution limit, several hundred pc) of one member galaxy in each of these systems is most probably falling toward the nucleus. Extended LINER-like emission with relatively broad lines---indicative of shock heating, probably due to collision of tidally stripped molecular clouds---is observed in two objects (ESO 253-IG026 and Kar 29). The nuclear spectra of the remaining two systems show dominant H ii emission associated with star formation, with some evidence suggesting a low-luminosity, obscured active nucleus. None of the four galaxy pairs hosts a luminous Seyfert 1 nucleus. The observed phenomenology---including the notable LINER-like emission---has apparently been produced within ~108 yr from the pair's closest approach. We may not be able to observe clear evidence of infall from ionized gas in Seyfert 1 galaxies if the inception of luminous, unobscured, type 1 activity requires a much longer timescale