A Very Large Array Search for Intermediate-Mass Black Holes in Globular Clusters in M81
Wrobel, J. M.
Miller-Jones, J. C. A.
MIddleton, M. J.
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Wrobel, J. M., Miller-Jones, J. C. A., & MIddleton, M. J. (2016). A Very Large Array Search for Intermediate-Mass Black Holes in Globular Clusters in M81. Astrophysical Journal https://doi.org/10.3847/0004-6256/152/1/22
Nantais et al. used the Hubble Space Telescope to localize probable globular clusters (GCs) in M81, a spiral galaxy at a distance of 3.63 Mpc. Theory predicts that GCs can host intermediate-mass black holes (IMBHs) with masses M_BH ∼ 100−100, 000 M_⊙. Finding IMBHs in GCs could validate a formation channel for seed BHs in the early universe, bolster gravitational-wave predictions for space missions, and test scaling relations between stellar systems and the central BHs they host. We used the NRAO Karl G. Jansky Very Large Array (VLA) to search for the radiative signatures of IMBH accretion from 206 probable GCs in a mosaic of M81. The observing wavelength was 5.5 cm and the spatial resolution was 1.5′′ (26.4 pc). None of the individual GCs are detected, nor are weighted-mean image stacks of the 206 GCs and the 49 massive GCs with stellar masses M⋆ ≳ 200, 000 M_⊙. We apply a semi-empirical model to predict the mass of an IMBH that, if undergoing accretion in the long-lived hard X-ray state, is consistent with a given radio luminosity. The 3σ radio-luminosity upper limits correspond to IMBH masses of M_BH(all) < 42, 000 M_⊙ for the all-cluster stack and M_BH(massive) < 51, 000 M_⊙ for the massive-cluster stack. We also apply the empirical fundamental-plane relation to two X-ray-detected clusters, finding that their individual IMBH masses at 95% confidence are M_BH < 99, 000 M_⊙ and M_BH < 15,000 M_⊙. Finally, no analog of HLX-1, a strong IMBH candidate in an extragalactic star cluster, occurs in any individual GC in M81. This underscores the uniqueness or rarity of the HLX-1 phenomenon.
black hole physics, galaxies: individual (M81), galaxies: star clusters: individual (M81, ESO 243-49 HLX-1, M60-UCD1), radio continuum: general
We thank the referee for a helpful and timely report, and Dr. E. Greisen for providing the new AIPS task stack. JCAMJ is the recipient of an Australian Research Council Future Fellowship (FT140101082). MJM acknowledges an Ernest Rutherford STFC fellowship (grant number RG77623). This research has made use of data obtained from the Chandra Source Catalog, provided by the Chandra X-ray Center (CXC) as part of the Chandra Data Archive. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.
External DOI: https://doi.org/10.3847/0004-6256/152/1/22
This record's URL: https://www.repository.cam.ac.uk/handle/1810/255944
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