A Very Large Array Search for Intermediate-Mass Black Holes in Globular Clusters in M81

Abstract

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 \sim 100 - 100,000 M_sun. 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 arcsec (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_star \gtrsim 200,000 M_sun. 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 3$\sigma$ radio-luminosity upper limits correspond to mean IMBH masses of M_BH(all) < 42,000 M_sun for the all-cluster stack and M_BH(massive) < 51,000 M_sun 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_sun and M_BH < 15,000 M_sun. 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.

23 pages; 7 figures; accepted by AJ

References in corpus (4)

• A Supermassive Black Hole in an Ultracompact Dwarf Galaxy
• Radio observations of NGC 2808 and other globular clusters: constraints on intermediate mass black holes
• Stacking of large interferometric data sets in the image- and uv-domain -- a comparative study
• On the radio properties of the intermediate-mass black hole candidate ESO 243-49 HLX-1

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• The Formation of Supermassive Black Holes from Population III.1 Seeds. I. Cosmic Formation Histories and Clustering Properties
• A consistency-test for determining whether ultra-compact dwarf galaxies could be the remnant nuclei of threshed galaxies
• Evolution and explosions of metal enriched supermassive stars: proton rich general relativistic instability supernovae
• Discovery of a radio transient in M81
• Accessing Intermediate-Mass Black Holes in 728 Globular Star Clusters in NGC\,4472
• A Chandra Survey of Milky Way Globular Clusters. III. Searching for X-ray Signature of Intermediate-mass Black Holes
• Planetary Systems in a Star Cluster II: intermediate-mass black holes and planetary systems
• A Search for Wandering Black Holes in the Milky Way with Gaia and DECaLS