Constraining Nuclear Molecular Gas Content with High-resolution CO Imaging of GOALS Galaxies

TL;DR

This study uses high-resolution ALMA CO imaging to measure nuclear molecular gas in merging galaxies, revealing significant gas masses that impact black hole mass estimates and challenge certain accretion models.

Contribution

It provides precise measurements of nuclear molecular gas in merging galaxies, refining black hole mass estimates and offering insights into gas dynamics near galactic centers.

Findings

Molecular gas masses of 3×10^7 to 6×10^8 M_sun within 70 pc of black holes.

Subtracting gas mass from enclosed mass aligns black hole estimates with scaling relations.

High-resolution CO imaging reveals gas masses that challenge simple accretion assumptions.

Abstract

We present measurements of the cool molecular gas mass around the nuclei of two gas-rich mergers, III Zw 035 and IRAS F01364-1042, whose enclosed masses (M$_\mathrm{enc}$) within the central 40-80 pc would be overmassive if attributed entirely to the supermassive black hole mass (SMBH) and compared to SMBH-galaxy scaling relations. Our gas mass measurements are derived from Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 long-baseline observations of CO(J=2-1) and 230 GHz continuum emission at 14-20 pc resolution, which probes below the resolving limit of the previous black hole mass measurements. Subtracting molecular gas mass from these enclosed masses is not enough to reconcile with BH-galaxy relationships, but independently measuring M$_\mathrm{enc}$ using the cold CO(2-1) gas does shift the black holes down to their expected values. Still, these ALMA data reveal respective molecular gas masses of $\sim$3$\times$10$^7$ to $\sim$6$\times$10$^8$ M$_\odot$ within 70 pc of these black holes, which could challenge some black hole accretion models that assume nuclear gas like this has no angular momentum.