Structure of the super-Eddington outflow and itsimpact on the cosmological scale

TL;DR

This study uses radiation hydrodynamic simulations to analyze super-Eddington outflows from high-redshift supermassive black holes, revealing anisotropic feedback effects that influence galaxy evolution.

Contribution

It presents a detailed two-dimensional simulation of super-Eddington outflows, connecting small-scale dynamics to larger scales, and highlights the anisotropic nature of black hole feedback.

Findings

Outflows reach velocities up to 0.7c near the black hole.

Mass outflow rate is about 30% of the injected mass.

Feedback impacts are stronger in face-on directions.

Abstract

It is one of the biggest issues in black hole (BH) astrophysics how to precisely evaluate BH feedback to its environments. Aiming at studying the unique gas dynamics of super-Eddington flow around supermassive black hole (SMBH) seeds at high redshift, we carried out axisymmetric two dimensional radiation hydrodynamic simulations by a nested simulation-box method. Here we divide the simulation box into the inner zone at $(2 - 3 \times 10^3) r_{\rm{Sch}}$ (with $r_{\rm Sch}$ being the Schwarzschild radius) and the outer zone at $(2\times 10^{3} - 3\times 10^6) r_{\rm{Sch}}$, with smooth connection of the physical quantities, such as gas density, velocity, and radiation energy. We start the calculation by injecting mass through the outer boundary of the inner zone at a constant rate of $\dot{M}_{\rm{inj}}=10^3L_{\rm{Edd}}/c^2$, where $L_{\rm{Edd}}$ is the Eddington luminosity and $c$ is the speed of light. A powerful outflow is generated in the innermost region and it propagates from the inner zone to the outer zone. The outflows are characterized by a velocity of 0.02$c$ (0.7$c$) and density of $10^{-17}$ ($10^{-19}$) g cm$^{-3}$ for near the edge-on (face-on) direction. The outflow is gradually accelerated as it travels by accepting radiation-pressure force. The final mass outflow rate at the outermost boundary is $\dot{M}_{\rm{out}}\sim 0.3 \times \dot{M}_{\rm{inj}}$. By extrapolating the outflow structure to a further larger scale, we find that the momentum and energy fluxes at $r \sim 0.1$ pc are $\sim 10-100 L_{\rm{Edd}}/c $ and $\sim 0.1-10 L_{\rm{Edd}}$, respectively. Moreover, we find that the impacts are highly anisotropic in the sense that larger impacts are given towards the face-on direction than in the edge-on direction. These results indicate that the BH feedback will more efficiently work on the interstellar medium than that assumed in the cosmological simulations.