Globular Clusters Hosting Intermediate-Mass Black Holes: No Mass-Segregation Based Candidates

Mario Pasquato, Paolo Miocchi, Sohn Bong Won, Young Wook Lee

    Research output: Contribution to journalArticlepeer-review

    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 sizable 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 binary-fraction measurements 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 a 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, which 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.

    Original languageEnglish (US)
    Article number135
    JournalAstrophysical Journal
    Volume823
    Issue number2
    DOIs
    StatePublished - Jun 1 2016

    Keywords

    • Methods: statistical
    • Stars: black holes
    • globular clusters: general

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science

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