N-body modelling of globular clusters: masses, mass-to-light ratios and intermediate-mass black holes

By H. Baumgardt. 2016

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We have determined the masses and mass-to-light ratios of 50 Galactic globular clusters by comparing their velocity dispersion and surface brightness profiles against a large grid of 900 N-body simulations of star clusters of varying initial concentration, size and central black hole mass fraction. Our models follow the evolution of the clusters under the combined effects of stellar evolution and two-body relaxation allowing us to take the effects of mass segregation and energy equipartition between stars self-consistently into account. For a subset of 16 wellobserved clusters, we also derive their kinematic distances. We find an average mass-to-light ratio of Galactic globular clusters of =1.98 ± 0.03, which agrees very well with the expected M/L ratio if the initial mass function (IMF) of the clusters was a standard Kroupa or Chabrier mass function. We do not find evidence for a decrease in the average mass-to-light ratio with metallicity. The surface brightness and velocity dispersion profiles of most globular clusters are incompatible with the presence of intermediate-mass black holes (IMBHs) with more than a few thousand M in them. The only clear exception is ω Cen, where the velocity dispersion profile provides strong evidence for the presence of a ~40 000 M IMBH in the centre of the cluster.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/11716e43e5bf645f89c252a5c706b4c90139e762

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Citations in the corpus

Nuclear star clusters (2009, background): “Black holes of even lower masses (crossing into the realm of intermediate-mass BHs) have been claimed to exist at the centers of the likely stripped NSCs G1 (Gebhardt et al. 2002), ωCen (Noyola et al. 2010), and M 54 (Ibata et al. 2009; Baumgardt 2017).”
Very massive stars, pair-instability supernovae and intermediate-mass black holes with the sevn code (2017, background): “The existence of IMBHs (mass between ∼ 100 M and ∼ 105 M ) is still matter of debate (Farrell et al. 2009; Strader et al. 2012; Lützgendorf et al. 2013; Lanzoni et al. 2013; Baumgardt 2017; Kızıltan et al. 2017; Zocchi et al. 2017).”
Mean proper motions, space orbits, and velocity dispersion profiles of Galactic globular clusters derived fromGaiaDR2 data (2018, methodology): “The details of the fitting procedure can be found in Baumgardt (2017) and Baumgardt & Hilker (2018).”
Observational evidence for intermediate-mass black holes (2017, background): “Baumgardt (2017) also found that the velocity dispersion profile of ω Centauri is best fitted by an IMBH of 104 M .”
Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST, and literature data (2021, methodology): “The best-fitting distance is determined by fitting each cluster with the grid of N -body models calculated by Baumgardt (2017) and Baumgardt & Hilker (2018).”
A catalogue of masses, structural parameters, and velocity dispersion profiles of 112 Milky Way globular clusters (2018, methodology): “Since they lack radial velocity information, masses and structural parameters for NGC 6101 and NGC 6254 were determined by fitting the absolute number of main sequence stars at different radii which Sollima & Baumgardt (2017) derived from the ACS Treasure project data.”