WISDOM Project -- XXVIII. Molecular gas measurement of the supermassive black hole mass of the galaxy NGC 1387

TL;DR

This study measures the mass of the supermassive black hole in galaxy NGC 1387 using high-resolution molecular gas observations and Bayesian modeling, confirming its consistency with known galaxy relations.

Contribution

First high-resolution ALMA observations of molecular gas kinematics used to measure SMBH mass in NGC 1387 with Bayesian modeling and stellar potential constraints.

Findings

SMBH mass of approximately 1.10 x 10^8 solar masses.

Detected a face-on, rotating molecular gas disc with a central depression.

Results align with the SMBH mass-stellar velocity dispersion relation.

Abstract

Supermassive black hole (SMBH) masses can be measured using molecular gas kinematics. Here we present high angular resolution ($0.12$ arcsec or $\approx11$ pc) Atacama Large Millimeter/submillimeter Array observations of the $^{12}$CO(2-1) line emission of the early-type galaxy NGC 1387. The observations reveal a face-on, regularly-rotating central molecular gas disc with a diameter of $\approx18$ arcsec ($\approx1.7$ kpc) and a central depression slightly larger than the SMBH sphere of influence. We forward model the CO data cube in a Bayesian framework with the \textsc{Kinematic Molecular Simulation} code, and use \textit{Hubble Space Telescope} data to constrain the stellar gravitational potential contribution to the molecular gas kinematics. We infer a SMBH mass of $1.10^{+1.71}_{-0.95}[\text{stat},3\sigma]^{+2.45}_{-1.09}[\text{sys}]\times10^8$ M$_\odot$ and a F160W-filter stellar mass-to-light ratio of $0.90^{+0.44}_{-0.35}[\text{stat}, 3\sigma]^{+0.46}_{-0.36}[\text{sys}]$ M$_\odot$/L$_{\odot,\text{F160W}}$. This SMBH mass is consistent with the SMBH mass -- stellar velocity dispersion relation.