Radiative Avalanche: Starburst-induced Fueling to Active Galactic Nuclei

Abstract

We propose a novel mechanism for fueling active galactic nuclei (AGNs), i.e., a radiative avalanche, which is mass accretion driven by radiation drag exerted by stellar radiation from circumnuclear starburst regions. If a surface layer of a rotating gas disk is irradiated by intensive starlight, then it could lose angular momentum via radiation drag, which would result in an avalanche of the layer as an inevitable consequence. Analyses show that in an optically thick regime, the mass accretion rate via this radiative avalanche is independent of not only the extinction coefficient of photon-absorbing matter but also the density distribution of the disk, and the maximal mass accretion rate is simply described as ${u{M}{705F}}$ --> ~ L*/c2 with L* being the bolometric luminosity of a starburst. An extraordinarily intensive starburst of 3 ? 1012 L?, for example, could produce ${u{M}{705F}}$ --> ~ 0.2 M? yr-1. In a disk containing dust, the accretion timescale could be as short as less than 108 yr. If the radiative avalanche feeds an accretion disk around a supermassive black hole, gravitational energy can be liberated with a luminosity of the same order as L*. In the present context, the intensity of radiative avalanche determines whether a starburst galaxy is destined to posses an AGN or not. The present model provides a solid physical mechanism deduced from first principles to account for the possible link between starburst activities and AGNs, which has been suggested by a number of observations.