The Supermassive Black Hole and Dark Matter Halo of NGC 4649 (M60)
  We apply the axisymmetric orbit superposition modeling to estimate the mass
of the supermassive black hole and dark matter halo profile of NGC 4649. We
have included data sets from the Hubble Space Telescope, stellar, and globular
cluster observations. Our modeling gives the black hole mass = 4.5 \pm 1.0 10^9
\Msun and M/L = 8.7 \pm 1.0 (or 8.0 \pm 0.9 after foreground Galactic
extinction is corrected). We confirm the presence of a dark matter halo, but
the stellar mass dominates inside the effective radius. The parameters of the
dark halo are less constrained due to the sparse globular cluster data at large
radii. We find that in NGC 4649 the dynamical mass profile from our modeling is
consistently larger than that derived from the X-ray data over most of the
radial range by roughly 60% to 80%. It implies that either some forms of
non-thermal pressure need to be included, the assumed hydrostatic equilibrium
may not be a good approximation in the X-ray modelings of NGC 4649, or our
assumptions used in the dynamical models are biased. Our new black hole mass is
about two times larger than the previous published value; the earlier model did
not adequately sample the orbits required to match the large tangential
anisotropy in the galaxy center. If we assume that there is no dark matter, the
results on the black hole mass and M/L do not change significantly, which we
attribute to the inclusion of HST spectra, the sparse globular cluster
kinematics, and a diffuse dark matter halo. Without the HST data, the
significance of the black hole detection is greatly reduced.
