THE MASS-DISTRIBUTION IN THE ELLIPTIC GALAXY NGC-3377 - EVIDENCE FOR A 2X10(8) M-CIRCLE-DOT BLACK-HOLE

This paper is a study of the mass distribution in the central 35 '' si milar or equal to 1.7 kpc of the E5 galaxy NGC 3377. Stellar rotation velocity and velocity dispersion profiles (seeing sigma = 0.''(20-0.' '(56) and V-band surface photometry (sigma = 0.''(20-0.'' 26) have be en obtained with the Canada-France-Hawaii Telescope. NGC 3377 is kinem atically similar to M32: the central kinematic gradients are steep. Th ere is an unresolved central rise in rotation velocity to V = 110 +/- 3 km s(-1) (internal error) at r = 1.'' 0. The apparent velocity dispe rsion rises from 95 +/- 2 km s(-1) at 1.'' 0 less than or equal to r < 4 '' to 178 +/- 10 km s(-1) at the center. To search for a central bl ack hole, we derive three-dimensional velocity and velocity dispersion fields that fit the above observations and Hubble Space Telescope sur face photometry after projection and seeing convolution. Isotropic mod els imply that the mass-to-light ratio rises by a factor of similar to 4 at r < 2 '', to M/L-V greater than or similar to 10. If the mass-to -light ratio of the stars, M/L-V = 2.4 +/- 0.2, is constant with radiu s, then NGC 3377 contains a central massive dark object (MDO), probabl y a black hole, of mass M. similar or equal to (1.8 +/- 0.8) x 10(8) M .. Several arguments suggest that NGC 3377 is likely to be nearly isot ropic. However, flattened anisotropic maximum entropy models can fit t he present data without an MDO. Therefore, the MDO detection in NGC 33 77 is weaker than those in our Galaxy, M31, M32, and NGC 3115.The abov e masses are corrected for the E5 shape of the galaxy and for the diff erence between velocity moments and velocities given by Gaussian fits to the line profiles. We show that the latter correction does not affe ct the strength of the MDO detection, but it slightly reduces M. and M /L-V. At 3 '' less than or similar to r less than or similar to 35 '', M/L-V is constant at similar to 2.4. Therefore, the inner parts of NG C 3377 are dominated by a normal old stellar population. In this ellip tical galaxy, as in the bulge-dominated galaxies NGC 3115 and NGC 4594 , halo dark matter is unimportant over a significant range in radius n ear the center.