Direct Collapse to Precursors of Supermassive Black Hole Seeds:Radiation-feedback-generated Outflows

TL;DR

This study uses high-resolution cosmological simulations to model radiation-driven outflows during the direct collapse phase leading to supermassive black hole seeds, revealing how outflows develop and escape from early halos.

Contribution

It provides detailed modeling of outflows and feedback mechanisms during the direct collapse process at unprecedented resolution, highlighting the potential for outflow breakout and observational signatures.

Findings

Outflows develop rapidly, forming hot cavities and dense shells.

Shells expand beyond the halo virial radius, escaping the central region.

Anisotropic accretion attenuates UV/X-ray radiation, affecting outflow dynamics.

Abstract

We use high-resolution zoom-in cosmological simulations to model outflow triggered by radiation and thermal drivers around the central mass accumulation during direct collapse within the dark matter (DM) halo. The maximal resolution is $1.3\times 10^{-5}$\,pc, and no restrictions are put on the geometry of the inflow/outflow. The central mass is considered {\it prior} to the formation of the supermassive black hole seed at a redshift of $z\sim 15.9$, and can constitute either a supermassive star (SMS) of $\sim 10^5\,M_\odot$ surrounded by a growing accretion disk or a self-gravitating disk. The radiation transfer is modeled using the ray-tracing algorithm. Due to the high accretion rate of $\sim 1\,M_\odot\,{\rm yr^{-1}}$ determined by the DM halo, accretion is mildly supercritical, resulting in mildly super-critical luminosity which has only a limited effect on the accretion rate, with the duty cycle of $\sim 0.9$. We observe a fast development of hot cavities, which quickly extend into polar funnels and expand dense shells. Within the funnels, fast winds, $\sim 10^3\,{\rm km\,s^{-1}}$, are mass-loaded by the accreting gas. We follow the expanding shells to $\sim 1$\,pc, when the shell velocity remains substantially, $\sim 5$ times, above the escape speed. The ionization cones formed by the central UV/X-ray completely ionize the cavities. Extrapolating the outflow properties shows that the halo material outside the shell will have difficulty stopping it. We therefore conclude that the expanding wind-driven shell will break out of the central parsec and will reach the halo virial radius. Finally, the anisotropic accretion flow on sub-parsec scales will attenuate the UV/soft X-rays on the H$_2$. Hence, the formation of funnels and powerful outflows around, e.g., SMS, can have interesting observational corollaries.