The role of large-scale dynamics and interactions of galaxies is clear for the starburst activity in galaxies (Kennicutt et al 1987; Sanders et al 1988). IRAS ultra-luminous galaxies are all mergers (Sanders & Mirabel 1996), and the fraction of interacting galaxies is increasing with LIR / LB. But the influence of global dynamics is less clear for AGN activity. The fraction of Seyfert and quasars is however increasing with infrared luminosity, from 4 to 45% (Kim et al 1998).
A large fraction of galaxies with radio jets (FRII) are interacting (Heckman et al 1986, Baum et al 1992). QSOs appear more than usual to interact with companions (Hutchings & Neff 1992; Hutchings & Morris 1995), and low-z quasars are mergers on HST images. Interactions are therefore efficient, but along years it has been very difficult to find any correlation between bars and nuclear activity. Are actually bars responsible for the fueling?