New Limits on an Intermediate Mass Black Hole in Omega Centauri: I. Hubble Space Telescope Photometry and Proper Motions

Details New Limits on an Intermediate Mass Black Hole in Omega Centauri: I. Hubble Space Telescope Photometry and Proper Motions New Limits on an Intermediate Mass Black Hole in Omega Centauri: I. Hubble Space Telescope Photometry and Proper Motions

2009-05-05

arxiv.org/abs/0905.0627v2

Astrophys.J.710:1032-1062,2010

Astronomy and Astrophysics

Astrophysics

Galaxy Astrophysics

27 pages, 28 figures, ApJ in press. v2 includes additions in response to referee comments

Scientific paper

10.1088/0004-637X/710/2/1032

We analyze data from the Hubble Space Telescope's Advanced Camera for Surveys of the globular cluster Omega Cen. We construct a photometric and proper-motion catalog using the GO-9442, GO-10252, and GO-10775 data sets. The 2.5- to 4-year baseline between observations yields a catalog of some 10^5 proper motions, with 53,382 high-quality measurements in a central field. We determine the cluster center to ~1-arcsecond accuracy using two different star-count methods, and a completely independent method using 2MASS images. We also determine the kinematical center of the proper motions, which agrees with the star-count center to within its uncertainty. The proper-motion dispersion of the cluster increases gradually inwards, but there is no variation in kinematics with position within the central ~15 arcsec: there is no dispersion cusp and no stars with unusually high velocities. We measure for the first time in any globular cluster the variation in proper-motion dispersion with mass along the main sequence, and find the cluster not yet to be in equipartition. Our proper-motion results do not confirm the arguments put forward by Noyola, Gebhardt & Bergmann to suspect an intermediate-mass black hole (IMBH) in Omega Cen. In Paper II we present new dynamical models for the high-quality data presented here, with the aim of putting quantitative contraints on the mass of any possible IMBH.

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