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

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.

24 pages, 8 figures