Fueling Low‐Level AGN Activity through Stochastic Accretion of Cold Gas

Using a simple description of feedback from black hole (BH) growth, wedevelop an analytic model for the fueling of Seyferts (low-luminosity AGN) andtheir relation to their host galaxies, Eddington ratio distributions, andcosmological evolution. We derive a solution for evolution of accretion ratesin a feedback-driven blast wave, applicable to large-scale outflows from brightquasars in galaxy mergers, low-luminosity AGN, and BHs in supernova remnants.Under the assumption that cold gas stochastically accretes onto a central SMBHat a rate set by the dynamics of that gas, our solution determines the Seyfertlight curve evolution. We use this to predict the Seyfert luminosity function(LF), duty cycles, lifetimes, and distribution of host morphologies, Eddingtonratios, and obscuration as a function of AGN luminosity and mass, and findagreement with observations at z=0. We consider the breakdown of contributionsfrom this and stellar wind accretion and merger-driven activity. We makespecific predictions for the weak evolution of the Seyfert LF with redshift (LFof non-merger driven activity), and for changes in both the slope and scatterof the M_BH-sigma relation at low-M_BH. Quiescent fueling dominates over a wideluminosity range (-14 > M_B > -22) at z=0, where most BH growth occurs aroundM_BH~10^7 M_sun, in S0 and Sa/b galaxies. However, quasar activity fromgas-rich mergers evolves more rapidly with redshift, and by z=1 quiescentfueling is important only at luminosities an order of magnitude or more belowthe LF break. Although non-merger driven fueling is important for BH growth andthe M_BH-sigma relation at low M_BH, it does not significantly contribute tothe total BH mass density or cosmological backgrounds.Comment: 37 pages, 9 figures. Submitted to ApJ