WISDOM Project -- VII. Molecular gas measurement of the supermassive black hole mass in NGC 7052

TL;DR

This study measures the mass of the supermassive black hole in NGC 7052 using high-resolution ALMA observations of molecular gas, providing a more accurate estimate than previous ionized gas methods.

Contribution

The paper demonstrates the effectiveness of molecular gas as a tracer for SMBH mass measurement with ALMA, achieving high spatial resolution and improved accuracy over prior ionized gas techniques.

Findings

SMBH mass of (2.5±0.3)×10^9 M_sun derived from molecular gas

Molecular gas observations resolve the SMBH-dominated region at 37 pc resolution

Central molecular gas deficit likely caused by tidal disruption due to gravitational gradient

Abstract

Supermassive black hole (SMBH) masses can be measured by resolving the dynamical influences of the SMBHs on spatially-resolved tracers of the central potentials. Modern long-baseline interferometers have enabled the use of molecular gas as such a tracer. We present here Atacama Large Millimeter/submillimeter Array observations of the elliptical galaxy NGC 7052 at 0.11 arcseconds (37 pc) resolution in the 12CO(2-1) line and 1.3mm continuum emission. This resolution is sufficient to resolve the region in which the potential is dominated by the SMBH. We forward model these observations, using a multi-Gaussian expansion of a Hubble Space Telescope F814W image and spatially-constant mass-to-light ratio to model the stellar mass distribution. We infer a SMBH mass of $2.5\pm0.3\times10^9\,\mathrm{M_\odot}$ and a stellar I-band mass-to-light ratio of $4.6\pm 0.2\,\mathrm{M_\odot/L_{\odot,I}}$ ($3\sigma$ confidence intervals). This SMBH mass is significantly larger than that derived using ionised gas kinematics, which however appear significantly more kinematically disturbed than the molecular gas. We also show that a central molecular gas deficit is likely to be the result of tidal disruption of molecular gas clouds due to the strong gradient in the central gravitational potential.