The central dynamics of M3, M13, and M92: Stringent limits on the masses
  of intermediate-mass black holes
  We used the PMAS integral field spectrograph to obtain large sets of radial
velocities in the central regions of three northern Galactic globular clusters:
M3, M13, and M92. By applying the novel technique of crowded field 3D
spectroscopy, we measured radial velocities for about 80 stars within the
central ~ 10 arcsec of each cluster. These are by far the largest spectroscopic
datasets obtained in the innermost parts of these clusters up to now. To obtain
kinematical data across the whole extent of the clusters, we complement our
data with measurements available in the literature. We combine our velocity
measurements with surface brightness profiles to analyse the internal dynamics
of each cluster using spherical Jeans models, and investigate whether our data
provide evidence for an intermediate-mass black hole in any of the clusters.
The surface brightness profiles reveal that all three clusters are consistent
with a core profile, although shallow cusps cannot be excluded. We find that
spherical Jeans models with a constant mass-to-light ratio provide a good
overall representation of the kinematical data. A massive black hole is
required in none of the three clusters to explain the observed kinematics. Our
1sigma (3sigma) upper limits are 5300 M_sun (12000 M_sun) for M3, 8600 M_sun
(13000 M_sun) for M13, and 980 M_sun (2700 M_sun) for M92. A puzzling
circumstance is the existence of several potential high velocity stars in M3
and M13, as their presence can account for the majority of the discrepancies
that we find in our mass limits compared to M92.
