Abstract
Evidence for links between galaxy interactions and both nuclear activity and star formation is briefly reviewed. A set of new observations has been designed to test several classes of models that have been suggested for such connections. Comparing the kinematics of paired spirals with their star-forming properties shows the following: There is no difference in either nuclear or disk star formation between galaxies undergoing direct and retrograde encounters, and very little difference as a function of projected separation out to 100 kiloparsecs. Connections are seen between the type of kinematic disturbance seen in the disk and the level of star formation (nuclear and disk), and with the maximum velocity amplitude of disturbances when scaled to the circular velocity. These facts are in accord with models where global instabilities are triggered by external perturbations, but not schemes that invoke cloud collisions or H I - 112 interactions without such driving instabilities. For Seyfert nuclei, most of the ones surveyed show remarkably large regions of rigid-body rotation, at a median radius of 2.1 kpc and extending in the most extreme cases to beyond 10 kpc (independent of the presence of a strong optical bar). The triggering of AGN, in this sample, appears to be connected to a global instability in the disk. Such an instability may in turn drive the other proposed mechanisms for gas transport and compression, such as collisions between giant molecular clouds or cloud compression in response to pressure changes in the surrounding diffuse ISM.
