On the role of minor galaxy mergers in the formation of active galactic nuclei

The large-scale (similar to 100 kpc) environments of Seyfert galaxies are n ot significantly different from those of non-Seyfert galaxies. In the conte xt of the interaction model of the formation of active galactic nuclei (AGN s), it has thus been proposed that AGNs form via "minor mergers" of large d isk galaxies with smaller companions. We test this hypothesis by comparing the nuclear spectra of 105 bright nearby galaxies with measurements of thei r R- or r-band morphological asymmetries at three successive radii. We find no significant differences between these asymmetries among the 13 Seyfert galaxies in the sample and galaxies having other nuclear spectral types (ab sorption, H II region-like, LINER), nor is there strong qualitative evidenc e that such mergers have occurred among any of the Seyfert galaxies or LINE Rs. Thus, either any minor mergers began greater than or similar to 1 Gyr a go and are essentially complete, or they did not occur at all, and AGNs for m independently of any type of interaction. Support for the latter interpre tation is provided by the growing evidence that supermassive black holes ex ist in the cores of most elliptical and early-type spiral galaxies, which i n turn suggests that nuclear activity represents a normal phase in the evol ution of the bulges of massive galaxies. Galaxy mergers may increase the lu minosity of Seyfert nuclei to the level of QSOs, which could explain why th e latter objects appear to be found in rich environments and in interacting systems.