Very Large Telescope Kinematics for Omega Centauri: Further Support for a Central Black Hole

Abstract

The Galactic globular cluster ω Centauri is a prime candidate for hosting an intermediate-mass black hole. Recent measurements lead to contradictory conclusions on this issue. We use VLT-FLAMES to obtain new integrated spectra for the central region of ω Centauri. We combine these data with existing measurements of the radial velocity dispersion profile taking into account a new derived center from kinematics and two different centers from the literature. The data support previous measurements performed for a smaller field of view and show a discrepancy with the results from a large proper motion data set. We see a rise in the radial velocity dispersion in the central region to 22.8 ± 1.2 km s^-1, which provides a strong sign for a central black hole. Isotropic dynamical models for ω Centauri imply black hole masses ranging from 3.0 × 10⁴ to 5.2 × 10⁴ M _sun depending on the center. The best-fitted mass is (4.7 ± 1.0) × 10⁴ M _sun.

Based on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere, Chile (085.D-0928).