Galaxy discs regulate the growth of supermassive black holes

TL;DR

This study uses the EAGLE simulation to explore how galaxy structure and halo properties influence supermassive black hole growth, highlighting the role of galaxy morphology and halo energy in regulating SMBH mass.

Contribution

It demonstrates that SMBH mass correlates more tightly with halo binding energy than with halo mass or stellar mass, emphasizing the importance of galaxy morphology and interactions.

Findings

SMBHs follow the observed $M_{\rm BH}$-$M_{\star}$ relation, varying with galaxy morphology.

$M_{\rm BH}$ correlates more tightly with halo binding energy ($E_{\rm bind}$) than with halo mass.

Galaxy mergers and interactions disrupt rotational support, enabling rapid SMBH growth.

Abstract

We examine the relationship between the mass of present-day central supermassive black holes (SMBHs, $M_{\rm BH}$), and the stellar mass ($M_{\star}$) and halo mass ($M_{200}$) of their host galaxies in the EAGLE simulation, and find that scatter about these relations correlates with both halo structure and galaxy morphology. EAGLE reproduces the observed $M_{\rm BH}$-$M_{\star}$ relation, including (qualitatively) its dependence on morphology: at fixed $M_{\star}$, disc-dominated galaxies host less massive SMBHs than ellipticals. We show that $M_{\rm BH}$ correlates with $M_{200}$, as expected if SMBHs are regulated by processes acting on the scale of the host dark matter halo, but exhibits a tighter correlation with the halo binding energy ($E_{\rm bind}$), signalling that this quantity, which encodes information about both halo mass and halo structure, is more fundamental to $M_{\rm BH}$. As with $M_{\rm BH}$-$M_{\star}$, scatter about the $M_{\rm BH}$-$E_{\rm bind}$ relation is strongly correlated with morphology. Gas in the central few parsecs of galaxies with present-day discs retains strong rotational support as the galaxy grows, inhibiting inward transport and precluding periods of rapid SMBH growth by gas accretion. In galaxies destined to be present-day ellipticals, however, this rotational support is disrupted, enabling gas to be funnelled onto the central SMBH, triggering rapid growth. Evolution of the mass fraction of stars formed ex-situ indicates that this disruption is caused by galaxy-galaxy interactions and mergers. Our findings corroborate the conclusion of recent studies, based on controlled simulations of an ~$L^{\star}$ galaxy, that prolonged secular galaxy evolution inhibits central SMBH growth.