2013ApJ...769..107L

By combining high spatial resolution and wide-field spectroscopy performed, respectively, with SINFONI and FLAMES at the ESO/VLT we measured the radial velocities of more than 600 stars in the direction of NGC 6388, a Galactic globular cluster which is suspected to host an intermediate-mass black hole. Approximately 55% of the observed targets turned out to be cluster members. The cluster velocity dispersion has been derived from the radial velocity of individual stars: 52 measurements in the innermost 2'', and 276 stars located between 18'' and 600''. The velocity dispersion profile shows a central value of ∼13 km/s, a flat behavior out to ∼60'' and a decreasing trend outward. The comparison with spherical and isotropic models shows that the observed density and velocity dispersion profiles are inconsistent with the presence of a central black hole more massive than ∼2000 M_☉. These findings are at odds with recent results obtained from integrated light spectra, showing a velocity dispersion profile with a steep central cusp of 23-25 km/s at r < 2'' and suggesting the presence of a black hole with a mass of ∼1.7x10⁴ M_☉. We also found some evidence of systemic rotation with amplitude A_rot∼ 8 km/s in the innermost 2'' (0.13 pc), decreasing to A_rot= 3.2 km/s at 18'' < r < 160''.