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Post Info TOPIC: NGC 5286
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RE: NGC 5286
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Title: Indication for an intermediate-mass black hole in the globular cluster NGC 5286 from kinematics
Authors: A. Feldmeier, N. Lützgendorf, N. Neumayer, M. Kissler-Patig, K. Gebhardt, H. Baumgardt, E. Noyola, P. T. de Zeeuw, B. Jalali

Intermediate-mass black holes (IMBHs, 10^2-10^5 solar masses) 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 favour 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) x 10^3 solar masses. 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) x 10^5 solar masses, which results in an IMBH mass of M_BH=(3.9±2.0) x 10^3 solar masses. 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.

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Blobrana


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Posts: 131433
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Title: The Globular Cluster NGC 5286. I. A New CCD BV Color-Magnitude Diagram
Authors: M. Zorotovic (1), M. Catelan (1), M. Zoccali (1), B. J. Pritzl (2), H. A. Smith (3), A. W. Stephens (4), R. Contreras (1,5), M. E. Escobar (1) ((1) PUC-Chile; (2) Univ. Wisconsin Oshkosh; (3) Michigan State Univ.; (4) Gemini Obs.; (5) INAF-Oss. Astr. Bologna)

We present BV photometry of the Galactic globular cluster NGC 5286, based on 128 V frames and 133 B frames, and covering the entire face of the cluster. Our photometry reaches almost two magnitudes below the turn-off level, and is accordingly suitable for an age analysis. Field stars were removed statistically from the cluster's colour-magnitude diagram (CMD), and a differential reddening correction applied, thus allowing a precise ridgeline to be calculated.
Using the latter, a metallicity of [Fe/H] = -1.70 ± 0.10 in the Zinn & West scale, and [Fe/H] = -1.47 ± 0.02 in the Carretta & Gratton scale, was derived on the basis of several parameters measured from the red giant branch, in good agreement with the value provided in the Harris catalogue.
Comparing the NGC 5286 CMD with the latest photometry for M3 by P. B. Stetson (2008, priv. comm.), and using VandenBerg isochrones for a suitable chemical composition, we find evidence that NGC 5286 is around 1.7 ± 0.9 Gyr older than M3. This goes in the right sense to help account for the blue horizontal branch of NGC 5286, for which we provide a measurement of several morphological indicators. If NGC 5286 is a bona fide member of the Canis Major dwarf spheroidal galaxy, as previously suggested, our results imply that the latter's oldest components may be at least as old as the oldest Milky Way globular clusters.

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