Science with an ngVLA: Precision Gas-dynamical Mass Measurement of
  Supermassive Black Holes with the ngVLA
  Emission line observations of circumnuclear gas disks in the ALMA era have
begun to resolve molecular gas tracer kinematics near supermassive black holes
(BHs), enabling highly precise mass determination in the best cases. The ngVLA
is capable of extremely high spatial resolution imaging of the CO(1-0)
transition at 115 GHz for nearby galaxies. Furthermore, its high (anticipated)
emission line sensitivity suggests this array can produce benchmark BH mass
measurements. We discuss lessons learned from gas-dynamical modeling of recent
ALMA data sets and also compare ALMA and ngVLA CO simulations of a dynamically
cold disk. While only a fraction of all local galaxies likely possess
sufficiently bright, regularly-rotating nuclear molecular gas, in such cases
the ngVLA is expected to more efficiently resolve such emission arising at a
projected 50-100 mas from the central BH.
