Matching Globular Cluster Models to Observations

Abstract

As ancient, gravitationally bound stellar populations, globular clusters represent abundant, vibrant laboratories, characterized by high frequencies of dynamical interactions, coupled to complex stellar evolution. Using surface brightness and velocity dispersion profiles from the literature, we fit 59 Milky Way globular clusters to dynamical models from the CMC Cluster Catalog. Without performing any interpolation, and without any directed effort to fit any particular cluster, 26 globular clusters are well matched by at least one of our models. We discuss in particular the core-collapsed clusters NGC 6293, NGC 6397, NGC 6681, and NGC 6624, and the non-corecollapsed clusters NGC 288, NGC 4372, and NGC 5897. As NGC 6624 lacks well-fitting snapshots on the main CMC Cluster Catalog, we run six additional models in order to refine the fit. We calculate metrics for mass segregation, explore the production of compact object sources such as millisecond pulsars, cataclysmic variables, low-mass X-ray binaries, and stellar-mass black holes, finding reasonable agreement with observations. In addition, closely mimicking observational cuts, we extract the binary fraction from our models, finding good agreement, except in the dense core regions of core-collapsed clusters. Accompanying this paper are a number of python methods for examining the publicly accessible CMC Cluster Catalog, as well as any other models generated using CMC.

White Dwarf Subsystems in Core-Collapsed Globular Clusters

“…In Rui et al (2021a), we presented a framework for comparing CMC models to observed clusters based on surface brightness and velocity dispersion profiles. As an application of this framework, we analyzed the CMC Cluster Catalog and identified best-fit models for dozens of GCs observed in the Milky Way (MW), including NGC 6397, which was examined in detail in this earlier study.…”

“…As an application of this framework, we analyzed the CMC Cluster Catalog and identified best-fit models for dozens of GCs observed in the Milky Way (MW), including NGC 6397, which was examined in detail in this earlier study. We direct the reader to Rui et al (2021a) for a more detailed discussion of our scheme for identifying best-fit models for a given observed system.…”

“…In this analysis, we start with the CMC simulation identified by Rui et al (2021a) as an effective match to present-day NGC 6397. The initial conditions for this simulation are shown as row 10 in Table 1.…”

“…In Figure 2, we show surface brightness and velocity dispersion profiles for all models in this study overlaid on observed profiles of NGC 6397 from Trager et al (1995), Watkins et al (2015), Hilker (2018), andBaumgardt et al (2019). For further discussion of how models are compared to observations, see Rui et al (2021a). In bold red, we show the model identified as the best fit to NGC 6397 (via the method in Rui et al 2021a), corresponding to simulation 17 from Table 1 at the final cluster snapshot.…”

“…To demonstrate these processes, we present a large set of N-body models representative of NGC 6397. These models build upon the analysis of Rui et al (2021a), which presented best-fit models for NGC 6397 and other clusters (on the basis of matches to the observed surface brightness and velocity dispersion profiles) from an extensive suite of models covering the parameter space of Milky Way GCs (the CMC Cluster Catalog; Kremer et al 2020b). We go on to examine broadly populations of WDs in clusters and discuss various physical processes made possible by the high WD densities expected in core-collapsed clusters like NGC 6397.…”