Do Circumnuclear Dense Gas Disks Drive Mass Accretion onto Supermassive Black Holes?

TL;DR

This study finds a strong correlation between dense molecular gas in circumnuclear disks and black hole accretion rates in Seyfert galaxies, suggesting CNDs play a key role in fueling supermassive black holes.

Contribution

It provides observational evidence linking CND dense gas mass to black hole accretion, and proposes a model for studying CND-scale accretion with ALMA.

Findings

Correlation between dense gas mass and accretion rate in Seyfert galaxies.

CND-scale gas correlates more tightly with accretion than larger scales.

Star formation in CNDs likely drives black hole mass accretion.

Abstract

We present a positive correlation between the mass of dense molecular gas ($M_{\rm dense}$) of $\sim 100$ pc scale circumnuclear disks (CNDs) and the black hole mass accretion rate ($\dot{M}_{\rm BH}$) in total 10 Seyfert galaxies, based on data compiled from the literature and an archive (median aperture $\theta_{\rm med}$ = 220 pc). A typical $M_{\rm dense}$ of CNDs is 10$^{7-8}$ $M_\odot$, estimated from the luminosity of the dense gas tracer, the HCN($1-0$) emission line. Because dense molecular gas is the site of star formation, this correlation is virtually equivalent to the one between nuclear star formation rate and $\dot{M}_{\rm BH}$ revealed previously. Moreover, the $M_{\rm dense}-\dot{M}_{\rm BH}$ correlation was tighter for CND-scale gas than for the gas on kpc or larger scales. This indicates that CNDs likely play an important role in fueling black holes, whereas $>$kpc scale gas does not. To demonstrate a possible approach for studying the CND-scale accretion process with the Atacama Large Millimeter/submillimeter Array (ALMA), we used a mass accretion model where angular momentum loss due to supernova explosions is vital. Based on the model prediction, we suggest that only the partial fraction of the mass accreted from the CND ($\dot{M}_{\rm acc}$) is consumed as $\dot{M}_{\rm BH}$. However, $\dot{M}_{\rm acc}$ agrees well with the total nuclear mass flow rate (i.e., $\dot{M}_{\rm BH}$ + outflow rate). Although these results are still tentative with large uncertainties, they support the view that star formation in CNDs can drive mass accretion onto supermassive black holes in Seyfert galaxies.