The Candidate Intermediate-Mass Black Hole in the Globular Cluster M54

TL;DR

This study investigates the presence of an intermediate-mass black hole in globular cluster M54 through multi-wavelength observations, finding no X-ray or radio evidence, and discusses implications for its accretion activity and environment.

Contribution

It provides new constraints on the candidate IMBH in M54 using Chandra, Hubble, and VLA data, challenging previous claims of its detection.

Findings

No X-ray counterpart detected for the candidate IMBH.

Radio luminosity of the candidate IMBH is below 3.6 x 10^29 ergs/s.

Two background galaxies identified as probes of M54's intracluster medium.

Abstract

Ibata et al. reported evidence for density and kinematic cusps in the Galactic globular cluster M54, possibly due to the presence of a 9400 solar-mass black hole. Radiative signatures of accretion onto M54's candidate intermediate-mass black hole (IMBH) could bolster the case for its existence. Analysis of new Chandra and recent Hubble Space Telescope astrometry rules out the X-ray counterpart to the candidate IMBH suggested by Ibata et al. If an IMBH exists in M54, then it has an Eddington ratio of L(0.3-8 keV) / L(Edd) < 1.4 x 10^(-10), more similar to that of the candidate IMBH in M15 than that in G1. From new imaging with the NRAO Very Large Array, the luminosity of the candidate IMBH is L(8.5 GHz) < 3.6 x 10^29 ergs/s (3 sigma). Two background active galaxies discovered toward M54 could serve as probes of its intracluster medium.