Constraining Intermediate-Mass Black Holes in Globular Clusters
  Decades after the first predictions of intermediate-mass black holes (IMBHs)
in globular clusters (GCs) there is still no unambiguous observational evidence
for their existence. The most promising signatures for IMBHs are found in the
cores of GCs, where the evidence now comes from the stellar velocity
distribution, the surface density profile, and, for very deep observations, the
mass-segregation profile near the cluster center. However, interpretation of
the data, and, in particular, constraints on central IMBH masses, require the
use of detailed cluster dynamical models. Here we present results from Monte
Carlo cluster simulations of GCs that harbor IMBHs. As an example of
application, we compare velocity dispersion, surface brightness and
mass-segregation profiles with observations of the GC M10, and constrain the
mass of a possible central IMBH in this cluster. We find that, although M10
does not seem to possess a cuspy surface density profile, the presence of an
IMBH with a mass up to 0.75% of the total cluster mass, corresponding to about
600 Msun, cannot be excluded. This is also in agreement with the surface
brightness profile, although we find it to be less constraining, as it is
dominated by the light of giants, causing it to fluctuate significantly. We
also find that the mass-segregation profile cannot be used to discriminate
between models with and without IMBH. The reason is that M10 is not yet
dynamically evolved enough for the quenching of mass segregation to take
effect. Finally, detecting a velocity dispersion cusp in clusters with central
densities as low as in M10 is extremely challenging, and has to rely on only
20-40 bright stars. It is only when stars with masses down to 0.3 Msun are
included that the velocity cusp is sampled close enough to the IMBH for a
significant increase above the core velocity dispersion to become detectable.
