Radio Continuum Observations of 47 Tucanae and Ω Centauri: Hints for Intermediate-Mass Black Holes?

Lu, T.; Kong, Albert

doi:10.1088/2041-8205/729/2/l25

Cited by 32 publications

(55 citation statements)

References 48 publications

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“…Most recently, Lu & Kong (2011) have found a 3σ peak in their 5.5 GHz radio map of ω Cen at a position consistent with the center measured by AvdM10. Deeper radio imaging is required to determine if this peak is real, but the discovery of such peaks at the centers of both ω Cen and 47 Tuc is notable (Lu & Kong 2011).…”

Section: Do Globular Clusters (Gcs) Harbor Intermediate-mass Black Hosupporting

confidence: 73%

“…Deeper radio imaging is required to determine if this peak is real, but the discovery of such peaks at the centers of both ω Cen and 47 Tuc is notable (Lu & Kong 2011).…”

Section: Do Globular Clusters (Gcs) Harbor Intermediate-mass Black Homentioning

confidence: 99%

“…An IMBH accreting at a low fraction of its Eddington luminosity should be welldescribed by an absorbed power-law (PL), the spectral model used in numerous IMBH studies (e.g., Ho et al 2003a,b;Miller-Jones et al 2012), and in modeling lowluminosity active galactic nuclei (AGN, e.g., Dong et al 7 This limit comes from the radio study of Lu & Kong (2011), not a dynamical study, since Brownian motion would wash out the peak in the velocity dispersion that provides dynamical evidence for an IMBH.…”

Section: Observations and Analysismentioning

confidence: 99%

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A DEEP CHANDRA X-RAY LIMIT ON THE PUTATIVE IMBH IN OMEGA CENTAURI

Haggard

Cool

Heinke

et al. 2013

ApJ

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We report a sensitive X-ray search for the proposed intermediate mass black hole (IMBH) in the massive Galactic cluster, ω Centauri (NGC 5139). Combining Chandra X-ray Observatory data from Cycles 1 and 13, we obtain a deep (∼ 291 ks) exposure of the central regions of the cluster. We find no evidence for an X-ray point source near any of the cluster's proposed dynamical centers, and place an upper limit on the X-ray flux from a central source of f X (0.5 − 7.0 keV) ≤ 5.0 × 10 −16 erg cm −2 s −1 , after correcting for absorption. This corresponds to an unabsorbed X-ray luminosity of L X (0.5 − 7.0 keV) ≤ 1.6 × 10 30 erg s −1 , for a cluster distance of 5.2 kpc, Galactic column density N H = 1.2 × 10 21 cm −2 , and powerlaw spectrum with Γ = 2.3. If a ∼ 10 4 M ⊙ IMBH resides in the cluster's core, as suggested by some stellar dynamical studies, its Eddington luminosity would be L Edd ∼ 10 42 erg s −1 . The new X-ray limit would then establish an Eddington ratio of L X /L Edd 10 −12 , a factor of ∼10 lower than even the quiescent state of our Galaxy's notoriously inefficient supermassive black hole Sgr A*, and imply accretion efficiencies as low as η 10 −6 − 10 −8 . This study leaves open three possibilities: either ω Cen does not harbor an IMBH or, if an IMBH does exist, it must experience very little or very inefficient accretion.

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Section: Do Globular Clusters (Gcs) Harbor Intermediate-mass Black Hosupporting

confidence: 73%

“…Deeper radio imaging is required to determine if this peak is real, but the discovery of such peaks at the centers of both ω Cen and 47 Tuc is notable (Lu & Kong 2011).…”

Section: Do Globular Clusters (Gcs) Harbor Intermediate-mass Black Homentioning

confidence: 99%

Section: Observations and Analysismentioning

confidence: 99%

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A DEEP CHANDRA X-RAY LIMIT ON THE PUTATIVE IMBH IN OMEGA CENTAURI

Haggard

Cool

Heinke

et al. 2013

ApJ

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“…All of their fluxes lead to very low upper limits on a possible black-hole mass. Further, Cseh et al (2010) and Lu & Kong (2011) investigated radio and X-ray emission in the globular clusters NGC 6388 and ω Centauri, respectively, and found upper limits of ∼1500 M for NGC 6388, and 1100−5200 M for ω Centauri. However, various assumptions about the gas accretion process, such as clumpyness of the gas distribution, accretion efficiency and the translation of X-ray fluxes to bolometric fluxes to black-hole masses, have to be made.…”

Section: Introductionmentioning

confidence: 99%

Limits on intermediate-mass black holes in six Galactic globular clusters with integral-field spectroscopy

Lützgendorf

Kissler-Patig

Gebhardt

et al. 2013

A&A

113

104

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Context. The formation of supermassive black holes at high redshift still remains a puzzle to astronomers. No accretion mechanism can explain the fast growth from a stellar mass black hole to several billion solar masses in less than one Gyr. The growth of supermassive black holes becomes reasonable only when starting from a massive seed black hole with mass on the order of 10 2 −10 5 M . Intermediate-mass black holes are therefore an important field of research. Especially the possibility of finding them in the centers of globular clusters has recently drawn attention. Searching for kinematic signatures of a dark mass in the centers of globular clusters provides a unique test for the existence of intermediate-mass black holes and will shed light on the process of black-hole formation and cluster evolution. Aims. We are investigating six galactic globular clusters for the presence of an intermediate-mass black hole at their centers. Based on their kinematic and photometric properties, we selected the globular clusters NGC 1851, NGC 1904 (M 79), NGC 5694, NGC 5824, NGC 6093 (M 80), and NGC 6266 (M 62). Methods. We used integral field spectroscopy to obtain the central velocity-dispersion profile of each cluster. In addition we completed these profiles with outer kinematic points from previous measurements for the clusters NGC 1851, NGC 1094, NGC 5824, and NGC 6093. We also computed the cluster photometric center and the surface brightness profile using HST data. After combining these datasets we compared them to analytic Jeans models. We used varying M/L V profiles for clusters with enough data points in order to reproduce their kinematic profiles in an optimal way. Finally, we varried the mass of the central black hole and tested whether the cluster is better fitted with or without an intermediate-mass black hole. Results. We present the statistical significance, including upper limits, of the black-hole mass for each cluster. NGC 1904 and NGC 6266 provide the highest significance for a black hole. Jeans models in combination with a M/L V profile obtained from N-body simulations (in the case of NGC 6266) predict a central black hole of M • = (3 ± 1) × 10 3 M for NGC 1904 and M • = (2 ± 1) × 10 3 M for NGC 6266. Furthermore, we discuss the possible influence of dark remnants and mass segregation at the center of the cluster on the detection of an IMBH.

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“…They concluded that the detected emission comes more likely from a low-mass X-ray binary (LMXB) with a stellar-mass black hole than from an IMBH. Recent studies found no significant radio sources in the center of ω Centauri (Lu & Kong 2011) and NGC 6388 (Cseh et al 2010). However, mass estimates from upper limits on radio emission require assumptions on the gas properties and accretion model.…”

Section: Introductionmentioning

confidence: 99%

Indication for an intermediate-mass black hole in the globular cluster NGC 5286 from kinematics

Feldmeier

Lützgendorf

Neumayer

et al. 2013

A&A

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Context. Intermediate-mass black holes (IMBHs) fill the gap between stellar-mass black holes and supermassive black holes (SMBHs). The existence of the latter is widely accepted, but there are only few detections of intermediate-mass black holes (10 2 −10 5 M ) so far. Simulations have shown that intermediate-mass black holes may form in dense star clusters, and therefore may still be present in these smaller stellar systems. Also, extrapolating the M • -σ scaling relation to lower masses predicts intermediatemass black holes in systems with σ ∼ 10−20 km s −1 such as globular clusters. Aims. We investigate the Galactic globular cluster NGC 5286 for indications of a central intermediate-mass black hole using spectroscopic data from VLT/FLAMES , velocity measurements from the Rutgers Fabry Perot at CTIO, and photometric data from HST/ACS. Methods. We compute the photometric center, a surface brightness profile, and a velocity-dispersion profile. 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. Results. Both the Jeans models and the N-body simulations favor the presence of a central black hole in NGC 5286 and our detection is at the 1-to 1.5-σ level. From the spherical Jeans models we obtain a best fit with black-hole mass M • = (1.5 ± 1.0) × 10 3 M . 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) × 10 5 M , which results in an IMBH mass of M • = (3.9 ± 2.0) × 10 3 M . Jeans models give values for the total cluster mass that are lower by up to 34% due to a lower value of M/L. Our test of the Jeans models with N-body simulation data shows that the discrepancy in the total cluster mass 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, which have lower velocities than fainter 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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Radio Continuum Observations of 47 Tucanae and Ω Centauri: Hints for Intermediate-Mass Black Holes?

Cited by 32 publications

References 48 publications

A DEEP CHANDRA X-RAY LIMIT ON THE PUTATIVE IMBH IN OMEGA CENTAURI

A DEEP CHANDRA X-RAY LIMIT ON THE PUTATIVE IMBH IN OMEGA CENTAURI

Limits on intermediate-mass black holes in six Galactic globular clusters with integral-field spectroscopy

Indication for an intermediate-mass black hole in the globular cluster NGC 5286 from kinematics

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