Accretion onto Intermediate-Mass Black Holes in Dense Protogalactic Clouds

Abstract

We present the first results from two-dimensional simulations of radiatively-efficient accretion of metal-free gas onto intermediate-mass black holes. We fix the shape of the spectral energy distribution of the radiation produced near the event horizon and study the structure of the irradiated low-angular-momentum accretion flow over three orders of magnitude in radius from the black hole, 10^{14}-10^{17} cm for a 100 M_sun black hole. The luminosity of the central source is made to be proportional to the rate at which gas accretes across the inner boundary, which we set just inside the sonic radius. We find that photoionization heating and radiation pressure modify the structure of the flow. When the ambient gas density is 10^7 cm^{-3}, accretion is intermittent and on average reduced to 32% of the Eddington-limited rate, two orders of magnitude below the "Bondi" rate evaluated ignoring radiation, in agreement with simplified theoretical models. Even if the vicinity of the black hole is supplied with high density gas, accretion is rendered inefficient through heating and radiation pressure.