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 (BH) and dark matter (DM) halo profile of NGC 4649. We have included data sets from the Hubble Space Telescope (HST), stellar, and globular cluster (GC) observations. Our modeling gives M(center dot) = (4.5 +/- 1.0) x 10(9) M(circle dot) and M/L(V,obs) = 8.7 +/- 1.0 (or M/L(V) = 8.0 +/- 0.9 after foreground Galactic extinction is corrected). We confirm the presence of a DM halo, but the stellar mass dominates inside the effective radius. The parameters of the dark halo are less constrained due to the sparse GC 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%-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 M(center dot) is about 2 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 DM, the results on the BH mass and M/L(V,obs) do not change significantly, which we attribute to the inclusion of HST spectra, the sparse GC kinematics, and a diffuse DM halo. Without the HST data, the significance of the BH detection is greatly reduced.