Hubble Space Telescope Proper Motion (HSTPROMO) Catalogs of Galactic Globular Clusters. VII. Energy Equipartition

Author(s): Laura L. Watkins, Roeland P. van der Marel, Mattia Libralato, Andrea Bellini, Jay Anderson, Mayte Alfaro-Cuello
Abstract: We examine the degree of energy equipartition in nine Galactic globular clusters using proper motions measured with the Hubble Space Telescope. For most clusters in the sample, this is the first energy equipartition study ever performed. This study is also the largest of its kind, albeit with only nine clusters. We begin by rigorously cleaning the catalogs to remove poor-quality measurements and to ensure high signal to noise for the study. Using the cleaned catalogs, we investigate how velocity dispersion σ changes with stellar mass m. We fit two functional forms: the first, a classic power law of the form σ ∝ m ^-η where η is the degree of energy equipartition, and the second from Bianchini et al. parameterized by an equipartition mass m _eq where η changes with stellar mass. We find that both functions fit well but cannot distinguish with statistical significance which function provides the best fit. All clusters exhibit varying degrees of partial equipartition; no cluster is at or near full equipartition. We search for correlations of η and m _eq with various cluster properties. The most significant correlation is observed with the number of core or median relaxation times (N_core or N _half) the cluster has experienced. Finally, we determine the radial equipartition profile for each cluster, that is, how the degree of equipartition changes with projected distance from the cluster center. We do not detect statistically significant trends in the degree of equipartition with radius. Overall, our observational findings are in broad agreement with theoretical predictions from N -body models published in recent years.
Organisation(s): Department of Astrophysics
External organisation(s): European Southern Observatory (Germany), Space Telescope Science Institute, Johns Hopkins University
Journal: The Astrophysical Journal
Volume: 936
ISSN: 0004-637X
DOI: https://doi.org/10.3847/1538-4357/ac77f7
Publication date: 09-2022
Peer reviewed: Yes
Austrian Fields of Science 2012: 103003 Astronomy, 103004 Astrophysics
Keywords
ASJC Scopus subject areas: Astronomy and Astrophysics, Space and Planetary Science
Portal url: https://ucrisportal.univie.ac.at/en/publications/2da11a62-2ce5-4e62-a3a3-f6a54b31b169

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