THE RELATION BETWEEN DYNAMICAL PERTURBATIONS, MORPHOLOGY, AND NUCLEAR ACTIVITY IN SPIRAL GALAXIES

摘要

The whole population of active galaxies with known morphology has been investigated. It is found, in agreement with earlier findings, that the vast majority of active nuclei appears in early-type spirals. The percentage of active nuclei in barred galaxies is similar to the percentage of barred galaxies in the general population of spirals. Even if active galaxies in general do not seem to prefer barred galaxies, it appears that all of them without exception either have a close companion or present a distorted morphology, usually with bars and/or rings. This result strongly suggests that the presence of nonaxisymmetric components of the potential is a necessary condition for the onset of nuclear activity. Arguments are also given to understand the connection between morphology and nuclear activity and on the sufficient conditions to produce it. The variety of situations leading to the presence of nonaxisymmetric perturbations strongly points out that the presence of nuclear activity is not the cause but one of the effects accompanying those perturbations.