Interactions are an essential mechanism in the fueling of QSOs, high-power radio-galaxies and ULIRgs. But they are not dominant in Seyferts and low- power radio-galaxies.
Observations reveal a close complicity between starbursts and AGN. AGN may be fueled by mass loss during PMS stellar evolution, of a coeval stellar cluster of 4 109 M, within 10pc (Norman & Scoville 1988). Within 108yr, mass loss accumulates 1.5 109 M. Radiation (UV, X) from the inner accretion disk ionizes stellar envelopes, and form the BLR (V ~ 3000 km/s in the black hole potential well). The young stellar cluster requires a huge starburst, like those due to mergers. Shocks are then inevitable, model-independent supernovae can help transfering angular momentum. Starbusrts and AGN are symbiotic systems (Collin et al 1988, Perry 1992, Williams et al 1999, Collin & Zahn 1999).