VLA Limits on Intermediate-mass Black Holes in 19 Massive Globular Clusters
Abstract
The NSF's Karl G. Jansky Very Large Array (VLA) was used at 3 cm to search for accretion signatures from intermediate-mass black holes (IMBHs) in 19 globular star clusters (GCs) in NGC 3115, an early-type galaxy at a distance of 9.4 Mpc. The 19 GCs have stellar masses M⋆ ∼ (1.1-2.7) × 106 M⊙, with a mean $\overline{{M}_{\star }}\sim 1.8\times {10}^{6}\,{M}_{\odot }$ . None were detected. An IMBH accretion model was applied to the individual GCs and their radio stack. The radio-stacked GCs have an IMBH mass $\overline{{M}_{\mathrm{IMBH}}}\lt 1.7\times {10}^{5}\,{M}_{\odot }$ and mass fraction $\overline{{M}_{\mathrm{IMBH}}}/\overline{{M}_{\star }}\lt 9.5 \% $ , with each limit being uncertain by a factor of about 2.5. The latter limit contrasts with the extremes of some stripped nuclei, suggesting that the set of stacked GCs in NGC 3115 is not a set of such nuclei. The radio luminosities of the individual GCs correspond to X-ray luminosities LX < (3.3-10) × 1038 erg s-1, with a factor of about 2.5 uncertainty. These limits predicted for putative IMBHs in the GCs are consistent with extant Chandra observations. Finally, a simulated observation with a next-generation VLA demonstrates that accretion signatures from IMBHs in GCs can be detected in a radio-only search, yet they elude detection in an X-ray-only search due to confusion from X-ray binaries in the GCs.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2020
- DOI:
- 10.3847/1538-4357/aba8f7
- arXiv:
- arXiv:2007.12093
- Bibcode:
- 2020ApJ...900..134W
- Keywords:
-
- intermediate-mass black holes;
- early-type galaxies;
- globular star clusters;
- aperture synthesis;
- Accretion;
- 816;
- 429;
- 656;
- 53;
- 14;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 8 pages, 4 figures, accepted 2020 July 22 by ApJ