A Multimass Velocity Dispersion Model of 47 Tucanae Indicates No Evidence for an Intermediate-mass Black Hole

Abstract

In this paper, we analyze stellar proper motions in the core of the globular cluster 47 Tucanae to explore the possibility of an intermediate-mass black hole (IMBH) influence on the stellar dynamics. Our use of short-wavelength photometry affords us an exceedingly clear view of stellar motions into the very center of the crowded core, yielding proper motions for >50,000 stars in the central 2 . We model the velocity dispersion profile of the cluster using an isotropic Jeans model. The density distribution is taken as a central IMBH point mass added to a combination of King templates. We individually model the general low-mass cluster objects (main-sequence/giant stars), as well as the concentrated populations of heavy binary systems and dark stellar remnants. Using unbinned likelihood model fitting, we find that the inclusion of the concentrated populations in our model plays a crucial role in fitting for an IMBH mass. The concentrated binaries and stellar-mass black holes (BHs) produce a sufficient velocity dispersion signal in the core so as to make an IMBH unnecessary to fit the observations. We additionally determine that a stellar-mass BH retention fraction of 8.5% becomes incompatible with our observed velocities in the core.

A consistency test for determining whether ultracompact dwarf galaxies could be the remnant nuclei of threshed galaxies

“…There has been an abundance of claims, usually followed by counter-claims, for the existence of IMBHs in large globular clusters. For example, see the studies of: G1, the most massive globular cluster around M31 (Gebhardt et al 2005;Miller-Jones et al 2012); ω Centauri, the most massive globular cluster around the Milky Way (Noyola et al 2008;Haggard et al 2013;Zocchi et al 2017Zocchi et al , 2019; plus other globular clusters around the Milky Way such as M15 (Gebhardt et al 2000;Gerssen et al 2002;Baumgardt et al 2003;Kirsten & Vlemmings 2012;den Brok et al 2014;Kirsten et al 2014); M54 (Ibata et al 2009); 47 Tucanae (Kızıltan et al 2017;Abbate et al 2018;Mann et al 2019);and NGC 6624 (Perera et al 2017;Gieles et al 2018;Baumgardt et al 2019). To date, there remains no conclusive evidence for IMBHs in globular clusters (Hurley 2007;Vesperini & Trenti 2010;Lanzoni & Cosmic-Lab Team 2016;Maccarone 2016;Wrobel et al 2016;Ferraro et al 2018;Tremou et al 2018), although see ).…”

Common-clock very long baseline interferometry using a coherent optical fiber link

“…Today, VLBI allows the most advanced imaging of our universe in the radio spectrum and, in turn, investigation of active galactic nuclei and black hole formation [24]. In geodesy, it allows positioning at millimeter precision level within the International Terrestrial Reference Frame (ITRF) [25] and the accurate investigation of global geodynamic phenomena and tectonic movements [26].…”

Soliton solution for the central dark mass in 47-Tuc globular cluster and implications for the axiverse

“…In order to compare our results with that of Ref. [27], we choose a King model as our stellar profile and we fix the effective core radius (a = 43.7 arcsec) and tidal radius (r t = 42 arcmin) to be the best fit given in King model. We take the distance of 47-Tuc from the earth (D = 4.69 kpc).…”

“…They are all presented in figure 6 in Ref. [27]. We preform a Markov Chain Monte Carlo (MCMC) analysis using the publicly available code [38] in two dimensions and estimate the value of the soliton mass and radius.…”

“…(Ref. [27]) who concluded ( at page 9, first column) that a concentration of stellar BHs with a scale of 2arcsec = 0.045pc can also explain the rising central velocity dispersion of the visible stars. Finally we plug the above constraints for the soliton Mass and Radius back in the mass-radius relation and estimate the axion mass as,…”