Kinematic Instabilities, Interactions, and Fueling of Seyfert Nuclei

Summary

ABSTRACT

I describe studies of the incidence of nuclear activity and star-formation rates for galaxies in two paired samples, as functions of the encounter direction and kinematic properties of the disturbed disk. One sample, designed to test star-formation diagnostics, is a geometrically derived subset of the Karachentsev catalog. A separate sample, of paired Seyferts, is used to search for common kinematic characteristics among interactiontriggered AGN. Both starbursts and Seyfert nuclei occur with about equal frequency in direct and retrograde encounters. Nuclear and disk star formation are correlated with the form of the velocity curve, and with the normalized amplitude of velocity disturbance in the disk. Seyfert nuclei in pairs show a high fraction of galaxies with large solid-body regions in the rotation curves. Such kinematic properties are associated with higher then normal star-formation rates in the K-pair spirals (but not the highest). For both AGN and starformation processes, the theoretical scheme most nearly accounting for the observations gives a prominent role to a Toomre-style disk instability on large scales, perhaps driving more local processes such as cloud collisions or pressure-induced cloud collapse. Including kinematic information offers a more refined way to identify externally-triggered phenomena than do disturbed morphology or presence of companions alone.