NEW LIMITS ON AN INTERMEDIATE-MASS BLACK HOLE IN OMEGA CENTAURI. II. DYNAMICAL MODELS

By R. P. van der Marel, Jay Anderson. 2009

166 citations recorded by the source corpus.

We present a detailed dynamical analysis of the projected density and kinematical data available for the globular cluster ω Centauri. We solve the spherical anisotropic Jeans equation for a given density profile to predict the projected profiles of the rms velocity , in each of the three orthogonal coordinate directions (line of sight, proper motion radial, and proper motion tangential). The models allow for the presence of a central dark mass, such as a possible intermediate-mass black hole (IMBH). We fit the models to new Hubble Space Telescope star count and proper motion data near the cluster center presented in the companion paper, which is Paper I in this series, combined with existing ground-based measurements at larger radii. The projected density profile is consistent with being flat near the center, with an upper limit γ ≲ 0.07 on the central logarithmic slope. The rms proper motion profile is also consistent with being flat near the center. The velocity anisotropy profile, distance, and stellar mass-to-light ratio are all tightly constrained by the data and found to be in good agreement with previous determinations by van de Ven et al. To fit the kinematics, we consider anisotropic models with either a flat core (γ = 0) or a shallow cusp (γ = 0.05). Core models provide a good fit to the data with MBH = 0; cusp models require a dark mass. If the dark mass in cusp models is an IMBH, then MBH = (8.7 ± 2.9) × 103 M☉; if it is a dark cluster, then its extent must be ≲0.16 pc. Isotropic models do not fit the observed proper motion anisotropy and yield spuriously high values for any central dark mass. These models do provide a good fit to the Gauss–Hermite moments of the observed proper motion distributions (h4 = −0.023 ± 0.004, h6 = 0.001 ± 0.004). There are no unusually fast-moving stars observed in the wings of the proper motion distribution, but we show that this does not strongly constrain the mass of any possible IMBH. The overall end result of the modeling is an upper limit to the mass of any possible IMBH in ω Centauri: MBH ≲ 1.2 × 104 M☉ at ∼1σ confidence (or ≲1.8 × 104 M☉ at ∼3σ confidence). The 1σ limit corresponds to MBH/Mtot ≲ 0.43%. We combine this with results for other clusters and discuss the implications for globular cluster IMBH demographics. Tighter limits will be needed to rule out or establish whether globular clusters follow the same black hole demographics correlations as galaxies. The arguments put forward by Noyola et al. to suspect an IMBH in ω Centauri are not confirmed by our study; the value of MBH they suggested is firmly ruled out.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/9fe8dedc06432857f692928bb7fc09756df8de5b

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In Astronomy and Astrophysics

1. Jay Anderson
2. G. Piotto
3. A. Milone
4. L. Bedin
5. F. D’Antona
6. A. Renzini
7. A. Marino
8. A. Aparicio

In Instrumentation

1. Jay Anderson
2. L. Bedin
3. A. Milone
4. G. Piotto
5. F. D’Antona
6. A. Renzini
7. A. Aparicio
8. Andrea Bellini

Citations in the corpus

• N-body modelling of globular clusters: masses, mass-to-light ratios and intermediate-mass black holes (2016, unknown): “In addition, van der Marel & Anderson (2010) found that anisotropic models provided a better fit to the velocity dispersion profile of ω Cen than isotropic models with central IMBHs.”
• Astrometry and Photometry with HST WFC3. II. Improved Geometric-Distortion Corrections for 10 Filters of the UVIS Channel (2011, background): “The globular cluster ω Cen has the largest internal-propermotion dispersion among Galactic globular clusters, despite being more than two times farther than the closest ones (4.7 kpc, van der Marel & Anderson 2010, vs. 2.2 kpc for M 4 and 2.3 kpc for NGC 6397, Harris 19969).”
• Observational evidence for intermediate-mass black holes (2017, background): “This is the case of another strong IMBH candidate in a globular cluster, ω Centauri, for which Noyola et al. (2008, 2010) claimed the presence of an IMBH of best-fitted mass (4.7±1.0)×104 M while van der Marel & Anderson (2010) reported an upper limit of 1.2 × 104 M .”
• MOCCA code for star cluster simulations – IV. A new scenario for intermediate mass black hole formation in globular clusters (2015, methodology): “Notwithstanding, several claims of their presence have been made, based on applying Jeans’ model to detaile photometric and spectroscopic data (e.g. Gebhardt, Rich & Ho 2005; van der Marel & Anderson 2010, and references therein).”
• THE HUBBLE SPACE TELESCOPE UV LEGACY SURVEY OF GALACTIC GLOBULAR CLUSTERS. I. OVERVIEW OF THE PROJECT AND DETECTION OF MULTIPLE STELLAR POPULATIONS (2014, background): “…of the radial velocity dispersion profiles, the velocity dispersion anisotropy, and possible rotation of many GCs. Dynamical modeling will constrain the mass profiles of the GCs, including the possible presence of intermediate-mass (≈ 103 – 104M⊙) black holes (van der Marel & Anderson 2010).”
• Nuclear star clusters (2009, background): “These dynamical detections are still debated (e.g., van der Marel and Anderson 2010; Miller-Jones et al. 2012; Tremou et al. 2018; Baumgardt et al. 2019), and further work at even higher spatial resolution is needed to reliably confirm or reject intermediate-mass black holes in these objects.”
• Galaxy Masses: A Review (2013, unknown): “At the present, this can be done for nearby star clusters by including plane-of-sky velocities from stellar proper motions in the dynamical models (e.g. van de Ven et al. 2006; van den Bosch et al. 2006; van der Marel & Anderson 2010).”