A Stellar Dynamical Measurement of the Black Hole Mass in the Maser Galaxy NGC 4258

Understand

We determine the mass of the black hole at the center of the spiral galaxy NGC 4258 by constructing axisymmetric dynamical models of the galaxy.

• These models are constrained by high spatial resolution imaging and long-slit spectroscopy of the nuclear region obtained with the {\em Hubble Space Telescope}, complemented by ground-based observations extending to larger radii.
• Our best mass estimate is $\MBH = (3.3 \pm 0.2) \times 10^7 \MSun $ for a distance of 7.28 Mpc (statistical errors only).
• This is within 15% of $ (3.82\pm 0.01) \times 10^7 \MSun$, the mass determined from the kinematics of water masers (rescaled to the same distance) assuming they are in Keplerian rotation in a warped disk.