Presentation #539.04 in the session “Black Holes and Accretion”.
Accurate measurements of the masses of supermassive black holes (SMBHs) are essential for understanding the coevolution of SMBHs and their host galaxies. Recently, the Atacama Large Millimeter/submillimeter Array (ALMA) has been shown to be a powerful tool to accurately determine SMBH masses in galaxies containing circumnuclear disks of cold molecular gas. In ALMA’s Cycle 3, we obtained 0.31 arcsec resolution CO(2-1) observations of the circumnuclear disk in the giant elliptical galaxy NGC 4786. The observations reveal a disk of radius 0.6 arcsec (200 pc) with kinematics dominated by regular rotation. We fit dynamical models directly to the ALMA data cube to constrain the gravitating mass distribution including the central black hole and a host galaxy model derived from Hubble Space Telescope near-infrared imaging. Model fits indicate a preliminary black hole mass of 9.6×108 Solar masses with approximately 13% statistical uncertainty. Future work will include an assessment of the systematic uncertainty in the mass model resulting from dust extinction in the central region of the host galaxy.