Evidence of a Supermassive Black Hole in the Galaxy NGC 1023 from the Nuclear Stellar Dynamics

We analyze the nuclear stellar dynamics of the SB0 galaxy NGC 1023, utilizingobservational data both from the Space Telescope Imaging Spectrograph aboardthe Hubble Space Telescope and from the ground. The stellar kinematics measuredfrom these long-slit spectra show rapid rotation (V = 70 km/s at a distance of0.1 arcsec = 4.9 pc from the nucleus) and increasing velocity dispersion towardthe nucleus (where sigma = 295 +/- 30 km/s). We model the observed stellarkinematics assuming an axisymmetric mass distribution with both two and threeintegrals of motion. Both modeling techniques point to the presence of acentral dark compact mass (which presumably is a supermassive black hole) withconfidence > 99%. The isotropic two-integral models yield a best-fitting blackhole mass of (6.0 +/- 1.4) x 10^7 M_sun and mass-to-light ratio (M/L_V) of 5.38+/- 0.08, and the goodness-of-fit (chi^2) is insensitive to reasonable valuesfor the galaxy's inclination. The three-integral models, whichnon-parametrically fit the observed line-of-sight velocity distribution as afunction of position in the galaxy, suggest a black hole mass of (3.9 +/- 0.4)x 10^7 M_sun and M/L_V of 5.56 +/- 0.02 (internal errors), and the edge-onmodels are vastly superior fits over models at other inclinations. The internaldynamics in NGC 1023 as suggested by our best-fit three-integral model showsthat the velocity distribution function at the nucleus is tangentiallyanisotropic, suggesting the presence of a nuclear stellar disk. The nuclearline of sight velocity distribution has enhanced wings at velocities >= 600km/s from systemic, suggesting that perhaps we have detected a group of starsvery close to the central dark mass.Comment: 21 pages, 12 figures, accepted in the Astrophysical Journa