Globular clusters hosting intermediate-mass black-holes: no mass-segregation based candidates

TL;DR

This study investigates globular clusters to identify potential intermediate-mass black hole hosts by analyzing mass-segregation and binary fractions, but finds no conclusive candidates, supporting the idea that these factors influence cluster dynamics.

Contribution

The paper combines multiple measurements of mass-segregation and binary fractions across several globular clusters to test for IMBH presence, providing a comprehensive analysis with no positive detections.

Findings

No suitable IMBH candidates found based on mass-segregation and binary fraction criteria.

Large core-to-half-mass radius ratios correlate with less mass-segregation and higher binary fractions.

Results support theoretical models where energy sources like IMBHs or binaries influence cluster core properties.

Abstract

Recently, both stellar mass-segregation and binary-fractions were uniformly measured on relatively large samples of Galactic Globular Clusters (GCs). Simulations show that both sizeable binary-star populations and Intermediate-Mass Black Holes (IMBHs) quench mass-segregation in relaxed GCs. Thus mass-segregation in GCs with a reliable binary-fraction measurement is a valuable probe to constrain IMBHs. In this paper we combine mass-segregation and binary-fraction measurements from the literature to build a sample of 33 GCs (with measured core-binary fractions), and a sample of 43 GCs (with a binary fraction measurement in the area between the core radius and the half-mass radius). Within both samples we try to identify IMBH-host candidates. These should have relatively low mass-segregation, a low binary fraction (< 5%), and short (< 1 Gyr) relaxation time. Considering the core binary fraction sample, no suitable candidates emerge. If the binary fraction between the core and the half-mass radius is considered, two candidates are found, but this is likely due to statistical fluctuations. We also consider a larger sample of 54 GCs where we obtained an estimate of the core binary fraction using a predictive relation based on metallicity and integrated absolute magnitude. Also in this case no suitable candidates are found. Finally, we consider the GC core- to half-mass radius ratio, that is expected to be larger for GCs containing either an IMBH or binaries. We find that GCs with large core- to half-mass radius ratios are less mass-segregated (and show a larger binary fraction), confirming the theoretical expectation that the energy sources responsible for the large core are also quenching mass-segregation