Evidence of Cross-Fueling in Active Galaxies

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.