Does black-hole growth depend fundamentally on host-galaxy compactness?

TL;DR

This study investigates whether black-hole growth is fundamentally linked to host-galaxy compactness by analyzing a large galaxy sample and controlling for confounding factors, finding limited dependence except possibly within central gas densities of star-forming galaxies.

Contribution

It provides a systematic partial-correlation analysis to disentangle the relationship between black-hole accretion and galaxy compactness, highlighting a potential link with central gas density in star-forming galaxies.

Findings

Black-hole accretion rate does not significantly depend on compactness when controlling for SFR or stellar mass.

In star-forming galaxies at z=0.5-1.5, a relation between BHAR and central density suggests a possible link to central gas density.

No strong dependence of BHAR on galaxy compactness in bulge-dominated or non-bulge galaxies.

Abstract

Possible connections between central black-hole (BH) growth and host-galaxy compactness have been found observationally, which may provide insight into BH-galaxy coevolution: compact galaxies might have large amounts of gas in their centers due to their high mass-to-size ratios, and simulations predict that high central gas density can boost BH accretion. However, it is not yet clear if BH growth is fundamentally related to the compactness of the host galaxy, due to observational degeneracies between compactness, stellar mass ($M_\bigstar$), and star formation rate (SFR). To break these degeneracies, we carry out systematic partial-correlation studies to investigate the dependence of sample-averaged BH accretion rate ($\rm \overline{BHAR}$) on the compactness of host galaxies, represented by the surface-mass density, $\Sigma_\rm e$, or the projected central surface-mass density within 1 kpc, $\Sigma_1$. We utilize 8842 galaxies with H < 24.5 in the five CANDELS fields at z = 0.5-3. We find that $\rm \overline{BHAR}$ does not significantly depend on compactness when controlling for SFR or $M_\bigstar$ among bulge-dominated galaxies and galaxies that are not dominated by bulges, respectively. However, when testing is confined to star-forming galaxies at z = 0.5-1.5, we find that the $\rm \overline{BHAR}$-$\Sigma_1$ relation is not simply a secondary manifestation of a primary $\rm \overline{BHAR}$-$M_\bigstar$ relation, which may indicate a link between BH growth and the gas density within the central 1 kpc of galaxies.