Indication for an intermediate-mass black hole in the globular cluster
  NGC 5286 from kinematics
  Intermediate-mass black holes (IMBHs, 10^2-10^5 M_sun) fill the gap between
stellar-mass black holes and supermassive black holes (SMBHs). Simulations have
shown that IMBHs may form in dense star clusters, and therefore may still be
present in these smaller stellar systems. We investigate the Galactic globular
cluster NGC 5286 for indications of a central IMBH using spectroscopic data
from VLT/FLAMES, velocity measurements from the Rutgers Fabry Perot at CTIO,
and photometric data from HST. We run analytic spherical and axisymmetric Jeans
models with different central black-hole masses, anisotropy, mass-to-light
ratio, and inclination. Further, we compare the data to a grid of N-body
simulations without tidal field. Additionally, we use one N-body simulation to
check the results of the spherical Jeans models for the total cluster mass.
Both the Jeans models and the N-body simulations favor the presence of a
central black hole in NGC 5286 and our detection is at the 1- to 1.5-sigma
level. From the spherical Jeans models we obtain a best fit with black-hole
mass M_BH=(1.5+-1.0)x10^3 M_sun. The error is the 68% confidence limit from
Monte Carlo simulations. Axisymmetric models give a consistent result. The best
fitting N-body model is found with a black hole of 0.9% of the total cluster
mass (4.38+-0.18)x10^5 M_sun, which results in an IMBH mass of
M_BH=(3.9+-2.0)x10^3 M_sun. Jeans models give lower values for the total
cluster mass. Our test of the Jeans models with N-body simulation data shows
that this discrepancy has two reasons: The influence of a radially varying M/L
profile, and underestimation of the velocity dispersion as the measurements are
limited to bright stars. We conclude that detection of IMBHs in Galactic
globular clusters remains a challenging task unless their mass fractions are
above those found for SMBHs in nearby galaxies. [abridged]
