We perform two-dimensional radiation hydrodynamical simulations of accretion flows onto a black hole (BH) with a mass of $10^3leq M_{rm BH}/M_{odot} lesssim 10^6$ in order to study rapid growth of BHs in the early Universe. For spherically symmetric flows, hyper-Eddington accretion onto the BH from outside the Bondi radius can occur unimpeded by radiation feedback only when the BH mass is higher than $simeq 10^4~M_{odot}(n_infty/10^5~{rm cm}^{-3})^{-1}(T_infty/10^4~{rm K})^{3/2}$, where $n_infty$ and $T_infty$ are the density and temperature of ambient gas. Here, we study the properties of accretion flows exposed to anisotropic radiation from a nuclear accretion disk with a luminosity higher than the Eddington value ($L_{rm Edd}$) due to collimation toward the bipolar directions. We find that, unlike the spherically symmetric case, even less massive BHs with $M_{rm BH} < 10^4~M_{odot}$ can be fed by surrounding gas at high accretion rates of $gtrsim L_{rm Edd}/c^2$ through the equatorial plane, while ionized regions expand to the polar directions producing hot outflows with $Tsim 10^5$K. For more massive BHs with $M_{rm BH}gtrsim 5times 10^5~M_{odot}$, neutral gas through the equatorial plane totally covers the central radiating region due to the non-radial gas motions, and thus the emergent radiation in all directions is blocked. Because of efficient recombination by hydrogen, the entire flow results in neutral and warm gas with $T simeq 8000~{rm K}$ . The central BH is fed through the equator at the averaged rate of $sim 5times 10^4~L_{rm Edd}/c^2$, which corresponds to $sim 50~%$ of the inflow rate from the Bondi radius. Moreover, radiation momentum absorbed by neutral hydrogen produces warm outflows toward the bipolar directions at $sim 30~%$ of the BH feeding rate and with a typical velocity of $simeq 50~{rm km~s}^{-1}$.
تحميل البحث