HUBBLE SPACE TELESCOPE PROPER MOTION (HSTPROMO) CATALOGS OF GALACTIC GLOBULAR CLUSTERS. II. KINEMATIC PROFILES AND MAPS

• Published in: The Astrophysical journal 2015-04, Vol.803 (1), p.1-22
• Main Authors: Watkins, Laura L, van der Marel, Roeland P, Bellini, Andrea, Anderson, Jay
• Format: Article
• Language: English
• Subjects: Anisotropy; Clusters; Correlation; Globular clusters; Hubble Space Telescope; Kinematics; Velocity distribution
• ISSN: 1538-4357; 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/803/1/29

We present kinematical analyses of 22 Galactic globular clusters using the Hubble Space Telescope proper motion catalogs recently presented in Bellini et al. For most clusters, this is the first proper-motion study ever performed, and, for many, this is the most detailed kinematic study of any kind. We use cleaned samples of bright stars to determine binned velocity-dispersion and velocity-anisotropy radial profiles and two-dimensional velocity-dispersion spatial maps. Using these profiles, we search for correlations between cluster kinematics and structural properties. We find the following: (1) more centrally concentrated clusters have steeper radial velocity-dispersion profiles; (2) on average, at 1[sigma] confidence in two dimensions, the photometric and kinematic centers of globular clusters agree to within ~1", with a cluster-to-cluster rms of 4"(including observational uncertainties); (3) on average, the cores of globular clusters have isotropic velocity distributions to within 1% ([sigma]t/[sigma]r = 0.992 + or - 0.005), with a cluster-to-cluster rms of 2% (including observational uncertainties); (4) clusters generally have mildly radially anisotropic velocity distributions (([sigma]t/[sigma]r [approx =] 0.8-1.0) near the half-mass-radius, with bigger deviations from isotropy for clusters with longer relaxation times; and (5) there is a relation between [sigma] sub(minor)/[sigma] sub(major) and ellipticity, such that the more flattened clusters in the sample tend to be more anisotropic, with [sigma] sub(minor)/[sigma] sub(major) [approx =] 0.9-1.0. Aside from these general results and correlations, the profiles and maps presented here can provide a basis for detailed dynamical modeling of individual globular clusters. Given the quality of the data, this is likely to provide new insights into a range of topics concerning globular cluster mass profiles, structure, and dynamics.