Feedback-regulated accretion onto the first black holes

Abstract

We study radiation-regulated gas accretion onto black holes (BHs) from galactic scales emphasizing the role of thermal and radiation pressures in limiting gas supply to the BH. We explore how the gas accretion depends on free parameters such as radiative efficiency, BH mass, ambient gas density/temperature, and the spectrum of the emitted radiation assuming simple initial conditions, as in the Bondi-Hoyle-Lyttleton problem. Our numerical simulations show an oscillatory behavior of the accretion rate, and thus the luminosity from the BH. We present a model for the feedback loop and provide analytical relationships for the accretion rate and the period of the accretion bursts. For stationary BHs the mean accretion rate is always less than 1% of the Bondi rate, and the period of the luminosity bursts is proportional to the average size of the ionized hot bubble. We discover that there are two distinct modes of oscillations with very different duty cycles (6% and 50%), governed by two different depletion processes of the gas inside the ionized bubble. We also study the growth rate and luminosity of BHs in motion with respect to their surrounding medium. Contrary to the case without radiation feedback, we find that the accretion rate increases with increasing BH velocity, v, reaching a maximum value at ν ∼ 25 km/s, before decreasing as ν−3. Moving BHs can grow faster than stationary BHs if the ambient gas temperature is < 104 K.