Molecular Gas in Major Mergers Hosting Dual and Single AGN at <10 kpc Nuclear Separations

TL;DR

This study uses high-resolution ALMA observations to analyze molecular gas in major galaxy mergers hosting dual and single AGN, revealing that non-rotating gas correlates with SMBH mass but not current accretion, and that dual AGN occurrence depends more on variability or obscuration than gas availability.

Contribution

It provides the first detailed kinematic analysis of molecular gas in local major mergers with dual and single AGN, highlighting the role of non-rotating gas and challenging assumptions about gas supply and AGN activity.

Findings

Higher SMBH mass correlates with more non-rotating molecular gas.

No significant difference in molecular gas mass between dual and single AGN hosts.

Dual AGN occurrence likely depends on variability or obscuration, not gas supply.

Abstract

We present high-resolution ($\sim$50$-$100 pc) Atacama Large Millimeter Array (ALMA) observations of $^{12}$CO(2-1) or $^{12}$CO(1-0) emission in seven local ($z$ $\lesssim$ 0.05) major mergers -- five of which are dual active galactic nuclei (AGN) systems, and two of which are single AGN systems. We model the molecular gas kinematics through rotating disk profiles using a Bayesian Markov chain Monte Carlo approach. The residuals were then used to isolate non-rotating components of the molecular gas -- the most likely contributor to future SMBH growth. We find that more massive SMBHs have higher surface densities of non-rotating molecular gas within their sphere of influence. This potential molecular gas supply, however, does not correlate with the current accretion efficiency of the SMBHs, suggesting that only a fraction of the observed non-rotating gas is currently reaching the SMBH. Finally, we tentatively find no significant differences in the nuclear molecular gas masses of single AGN and dual AGN hosts, both within the SMBH sphere of influence and within the central kiloparsec. Our results indicate that the probability of occurrence of the dual AGN phenomenon is likely dependent on AGN variability and/or obscuration rather than the availability of molecular gas in the nuclear regions.