The Mass Distribution in the Elliptical Galaxy NGC 3377: Evidence for a 2 × 10[TSUP]8[/TSUP] [ITAL]M[/ITAL][TINF][sun][/TINF] Black Hole

We have measured the mass distribution in the central 35" = 1.7 kpc of the E5galaxy NGC 3377. Stellar rotation velocity and velocity dispersion profiles(seeing sigma_* = 0.20 - 0.56 arcsec) and V-band surface photometry (sigma_* =0.20 - 0.26 arcsec) have been obtained with the Canada-France-Hawaii Telescope.NGC 3377 is kinematically similar to M32: the central kinematic gradients aresteep. The apparent velocity dispersion rises from 95 +- 2 km/s at 1" <= r <=4" to 178 +- 10 km/s at the center. To search for a central black hole, wederive three-dimensional velocity and velocity dispersion fields that fit ourobservations and Hubble Space Telescope surface photometry after projection andseeing convolution. Isotropic models imply that the mass-to-light ratio risesby a factor of ~ 4 at r < 2" to M/L_V > 10. If the mass-to-light ratio of thestars is constant with radius, then NGC 3377 contains a central massive darkobject (MDO), probably a black hole, of mass (1.8 +- 0.8) x 10**8 M_Sun.Several arguments suggest that NGC 3377 is likely to be nearly isotropic.However, flattened, anisotropic maximum entropy models can fit the data withoutan MDO. Therefore the MDO detection in NGC 3377 is weaker than those in M31,M32, or NGC 3115. The above MDO mass is corrected for the E5 shape of thegalaxy and for the difference between velocity moments and velocities given byGaussian fits to the line profiles. We show that the latter correction does notaffect the strength of the MDO detection, but it slightly reduces the mass andmass-to-light ratio. At 3" <= r <= 35", M/L_V is constant at ~ 2.4. Thereforethe inner parts of NGC 3377 are dominated by a normal old stellar population,not by halo dark matter.Comment: 20 pages, 17 figs, 4 tables, TeX, AJ, in press (May 1998