The dynamics of the dwarf elliptical galaxy FS 76: Bridging the kinematic dichotomy between elliptical and dwarf elliptical galaxies

We present major- and minor-axis kinematics out to approximate to2 half-light radii for the bright (M-B = -16.7) dwarf elliptical galaxy (dE) FS 76, a member of the NGC 5044 group. Its velocity dispersion is 46 +/- 2 km s(-1) in the center and rises to 70 +/- 10 km s(-1) at half-light radius. Beyond 1R(e), the dispersion starts to fall again. The maximum rotation velocity is 15 +/- 6 km s(-1), about the value expected for an oblate isotropic rotator with the same flattening as FS 76 (i.e., E1). Hence, FS 76 is the first dE discovered so far that is not flattened predominantly by anisotropy. There is a discontinuity in the radial velocity profile at +/- 1", corresponding to a kinematically peculiar core with a radial extent of 0.25 kpc. The reversed outward trend of the velocity dispersion is interpreted as evidence for a truncated dark halo and hence for the occurrence of tidal stripping. Using dynamical models, we estimate the total mass within a sphere of 1 kpc (approximate to1.5R(e)) to be between 1.2 and 3.4 x 10(9) M. at the 90% confidence level, corresponding to 3.2 greater than or equal to (M/L)(B)less than or equal to9.1. These values are consistent with predictions based on cold dark matter cosmological scenarios for galaxy formation.