The Black-Hole Mass in M87 from Gemini/NIFS Adaptive Optics Observations
  We present the stellar kinematics in the central 2" of the luminous
elliptical galaxy M87 (NGC 4486), using laser adaptive optics to feed the
Gemini telescope integral-field spectrograph, NIFS. The velocity dispersion
rises to 480 km/s at 0.2". We combine these data with extensive stellar
kinematics out to large radii to derive a black-hole mass equal to
(6.6+-0.4)x10^9 Msun, using orbit-based axisymmetric models and including only
the NIFS data in the central region. Including previously-reported ground-based
data in the central region drops the uncertainty to 0.25x10^9 Msun with no
change in the best-fit mass; however, we rely on the values derived from the
NIFS-only data in the central region in order to limit systematic differences.
The best-fit model shows a significant increase in the tangential velocity
anisotropy of stars orbiting in the central region with decreasing radius;
similar to that seen in the centers of other core galaxies. The black-hole mass
is insensitive to the inclusion of a dark halo in the models --- the high
angular-resolution provided by the adaptive optics breaks the degeneracy
between black-hole mass and stellar mass-to-light ratio. The present black-hole
mass is in excellent agreement with the Gebhardt & Thomas value, implying that
the dark halo must be included when the kinematic influence of the black hole
is poorly resolved. This degeneracy implies that the black-hole masses of
luminous core galaxies, where this effect is important, may need to be
re-evaluated. The present value exceeds the prediction of the black
hole-dispersion and black hole-luminosity relations, both of which predict
about 1x10^9 Msun for M87, by close to twice the intrinsic scatter in the
relations. The high-end of the black hole correlations may be poorly determined
at present.
