How Black Holes Stop Their Host Galaxy from Growing Without AGN Feedback

TL;DR

This paper explores how seed black holes from direct collapse influence early galaxy growth, showing they suppress star formation and cause deviations from local black hole-stellar mass relations without requiring active feedback.

Contribution

It demonstrates that seed black holes can inhibit star formation and alter galaxy evolution in the early universe without direct feedback mechanisms.

Findings

Seed black holes reduce gravitational instabilities in host galaxy discs.

Galaxies at z~6 lie above the local BH-stellar mass relation.

Slower black hole growth delays star formation by ~100 Myr.

Abstract

Super-massive black holes (SMBHs) with $M_{\bullet} \sim 10^9 $ M$_{\odot}$ at $z>6$ likely originate from massive seed black holes (BHs). We investigate the consequences of seeding SMBHs with direct collapse BHs (DCBHs) ($M_{\bullet}=10^{4-6}\, \mathrm{M}_\odot$) on proto-galactic disc growth. We show that even in the absence of direct feedback effects, the growth of seed BHs reduces the development of gravitational instabilities in host galaxy discs, suppressing star formation and confining stars to a narrow ring in the disc and leading to galaxies at $z \sim 6$ which lie above the local BH-stellar mass relation. The relative magnitude of cosmic and BH accretion rates governs the evolution of the BH-stellar mass relation. For typical DCBH formation epochs, $z_{\rm{i}} \sim 10$, we find star formation is inhibited in haloes growing at the average rate predicted by $\Lambda$CDM which host BHs capable of reaching $M_{\bullet}\sim 10^9 \, \mathrm{M}_{\odot}$ by $z\gtrsim6$. Slower growing BHs cause a delay in the onset of star formation; a $M_{\bullet} \sim 10^6 $ M$_{\odot}$ seed growing at $0.25$ times the Eddington limit will delay star formation by $\sim100$ Myr. This delay is reduced by a factor of $\sim10$ if the halo growth rate is increased by $\sim 0.6\, \sigma$. Our results suggest that SMBHs seeded by DCBHs and their host galaxies form in separate progenitor haloes. In the absence of subsequent mergers, higher than average cosmic accretion or earlier seed formation ($z_{\rm i} \sim 20$) are required to place the evolving BH on the local BH-stellar mass relation by $z=6$.