Enhanced direct collapse due to Lyman alpha feedback

TL;DR

This paper investigates how trapped Lyman alpha radiation influences the formation of direct collapse black holes, revealing it can significantly lower the required radiation threshold and increase their early universe abundance.

Contribution

It demonstrates that Lyman alpha feedback reduces the critical flux for DCBH formation, suggesting a higher expected number density of early universe black holes.

Findings

Lyman alpha photons lower the critical flux for DCBH formation.

Photodetachment of H- by Lyman alpha is most impactful at high background temperatures.

Supports DCBH as seeds for high-redshift quasars.

Abstract

We assess the impact of trapped Lyman alpha cooling radiation on the formation of direct collapse black holes (DCBHs). We apply a one-zone chemical and thermal evolution model, accounting for the photodetachment of H- ions, precursors to the key coolant H2, by Lyman alpha photons produced during the collapse of a cloud of primordial gas in an atomic cooling halo at high redshift. We find that photodetachment of H- by trapped Lyman alpha photons may lower the level of the H2-dissociating background radiation field required for DCBH formation substantially, dropping the critical flux by up to a factor of a few. This translates into a potentially large increase in the expected number density of DCBHs in the early Universe, and supports the view that DCBHs may be the seeds for the BHs residing in the centers of a significant fraction of galaxies today. We find that detachment of H- by Lyman alpha has the strongest impact on the critical flux for the relatively high background radiation temperatures expected to characterize the emission from young, hot stars in the early Universe. This lends support to the DCBH origin of the highest redshift quasars.