Hubble Space Telescope Proper Motion (HSTPROMO) Catalogs of Galactic Globular Clusters. V. The Rapid Rotation of 47 Tuc Traced and Modeled in Three Dimensions^*

Abstract

High-precision proper motions of the globular cluster 47 Tuc have allowed us to measure for the first time the cluster rotation in the plane of the sky and the velocity anisotropy profile from the cluster core out to about 13 ′ . These profiles are coupled with prior measurements along the line of sight and the surface-brightness profile, and fit all together with self-consistent models specifically constructed to describe quasi-relaxed stellar systems with realistic differential rotation, axisymmetry and pressure anisotropy. The best-fit model provides an inclination angle i between the rotation axis and the line-of-sight direction of 30 • , and is able to simultaneously reproduce the full three-dimensional kinematics and structure of the cluster, while preserving a good agreement with the projected morphology. Literature models based solely on line-of-sight measurements imply a significantly different inclination angle (i = 45 • ), demonstrating that proper motions play a key role in constraining the intrinsic structure of 47 Tuc. Our best-fit global dynamical model implies an internal rotation higher than previous studies have shown, and suggests a peak of the intrinsic V /σ ratio of ∼0.9 at around two half-light radii, with a non-monotonic intrinsic ellipticity profile reaching values up to 0.45. Our study unveils a new degree of dynamical complexity in 47 Tuc, which may be leveraged to provide new insights into the formation and evolution of globular clusters.

The Strong Rotation of M5 (NGC 5904) as Seen from the MIKiS Survey of Galactic Globular Clusters

“…As apparent, the stellar density distribution has spherical symmetry in the center and becomes increasingly flattened in the direction perpendicular to the rotation axis for increasing radius. Qualitatively, this trend is consistent with the model predictions of stellar systems flattened by rotation (e.g., Lupton & Gunn 1987;Varri & Bertin 2012) and found in the observational study of 47 Tucanae (Bianchini et al 2013;Bellini et al 2017;Heyl et al 2017). For the two outermost ellipses shown in the figure (at r ∼ 80″ and r ∼ 120″), we measure 1−b/a=0.1 and 0.14, where a and b are the major and the minor axes, respectively.…”

“…Rotation patterns as clear as those found in M5 have been detected just in a few other cases so far (see the cases of NGC 4372 in Kacharov et al 2014, and 47 Tucanae in Bellini et al 2017). However, evidence of systemic rotation signatures is mounting, with the most recent results for nine GCs presented in Ferraro et al (2018a; but see also Bellazzini et al 2012;Fabricius et al 2014;Kacharov et al 2014;Kimmig et al 2015;Bellini et al 2017;Boberg et al 2017;Kamann et al 2018, and references therein).…”

“…However, evidence of systemic rotation signatures is mounting, with the most recent results for nine GCs presented in Ferraro et al (2018a; but see also Bellazzini et al 2012;Fabricius et al 2014;Kacharov et al 2014;Kimmig et al 2015;Bellini et al 2017;Boberg et al 2017;Kamann et al 2018, and references therein). As shown by a number of theoretical studies (e.g., Fiestas et al 2006;Tiongco et al 2017; see also Figure 13), internal dynamical evolution and stellar escape cause a gradual loss of the initial cluster internal rotation.…”

“…Indeed, deviations from the sharply truncated King phase space distribution (e.g., see the cases of NGC 1851, as studied by Olszewski et al 2009;Marino et al 2014, NGC 5694 by Correnti et al 2011;Bellazzini et al 2015, and several others, as discussed, e.g., by Carballo-Bello et al 2018), spherical symmetry (e.g., Chen & Chen 2010), and pressure isotropy (e.g., van de Ven et al 2006;Bellini et al 2014Bellini et al , 2017Watkins et al 2015) are found in a growing number of GGCs. Also the observational evidence of systemic rotation is increasing (e.g., Anderson & King 2003;Lane et al 2009Lane et al , 2010Bellazzini et al 2012;Bianchini et al 2013;Fabricius et al 2014;Kacharov et al 2014;Kimmig et al 2015;Lardo et al 2015;Bellini et al 2017;Boberg et al 2017;Cordero et al 2017;Ferraro et al 2018b;Kamann et al 2018), possibly suggesting that, when properly surveyed, the majority of GCs rotate at some level. In particular, Ferraro et al (2018b) investigated the intermediate/external region of 11 clusters, demonstrating the presence of internal rotation in almost all of them.…”

The HST Large Programme on ω Centauri. II. Internal Kinematics

“…The authors attribute the presence of the skew to differential rotation of stars in the field. 47Tuc is characterized by a high clockwise rotation in the plane of the sky (see Bellini et al 2017c), with a peak of the intrinsic rotational velocity over velocity dispersion s V of ∼0.9 at around two r h , which is where the outer field of Heyl et al (2017) lies. Also the GC ωCen is known to be rotating (counterclockwise in this case) in the plane of the sky (e.g., van Leeuwen et al 2000;van de Ven et al 2006;Watkins et al 2013), so the presence of skewness in the m tan distribution should not come as a surprise.…”