Internal Stellar Kinematics of M32 from the SPLASH Survey: Dark Halo
  Constraints and the Formation of Compact Elliptical Galaxies
  As part of the SPLASH survey of the Andromeda galaxy (M31) and its neighbors,
we have obtained Keck/DEIMOS spectra of the compact elliptical (cE) satellite
M32. This is the first resolved-star kinematical study of any cE galaxy. In
contrast to previous studies that extended out to r<30"~1Re~100pc, we measure
the rotation curve and velocity dispersion profile out to r~250" and higher
order Gauss-Hermite moments out to r~70". We achieve this by combining
integrated-light spectroscopy at small radii (where crowding/blending are
severe) with resolved stellar spectroscopy at larger radii, using spatial and
kinematical information to statistically account for M31 contamination. The
rotation curve and velocity dispersion profile extend well beyond the radius
(r~150") where the isophotes are distorted. Unlike NGC 205, another close dwarf
companion of M31, M32's kinematic are regular and symmetric and do not show
obvious sharp gradients across the region of isophotal elongation and twists.
We interpret M32's kinematics using three-integral axisymmetric dynamical
equilibrium models constructed using Schwarzschild's orbit superposition
technique. Models with a constant M/L can fit the data remarkably well.
However, since such a model requires an increasing tangential anisotropy with
radius, invoking the presence of an extended dark halo may be more plausible.
Such an extended dark halo is definitely required to bind a half-dozen
fast-moving stars observed at the largest radii, but these stars may not be an
equilibrium component of M32. The observed regularity of the stellar
kinematics, as well as the possible detection of an extended dark halo, are
unexpected if M31 tides are significant at large radii. While these findings by
themselves do not rule out tidal models for cE formation, they suggest that
tidal stripping may not be as significant for shaping cE galaxies as has often
been argued.
