TY - JOUR

T1 - Globular Clusters Hosting Intermediate-Mass Black Holes

T2 - No Mass-Segregation Based Candidates

AU - Pasquato, Mario

AU - Miocchi, Paolo

AU - Won, Sohn Bong

AU - Lee, Young Wook

N1 - Funding Information:
National Research Foundation of Korea to the Center for Galaxy Evolution Research (No. 2010-0027910
Publisher Copyright:
© 2016. The American Astronomical Society. All rights reserved..

PY - 2016/6/1

Y1 - 2016/6/1

N2 - 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.

AB - 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.

KW - Methods: statistical

KW - Stars: black holes

KW - globular clusters: general

UR - http://www.scopus.com/inward/record.url?scp=84975119937&partnerID=8YFLogxK

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U2 - 10.3847/0004-637X/823/2/135

DO - 10.3847/0004-637X/823/2/135

M3 - Article

AN - SCOPUS:84975119937

SN - 0004-637X

VL - 823

JO - Astrophysical Journal

JF - Astrophysical Journal

IS - 2

M1 - 135

ER -