Hubble Space Telescope Proper Motion (HSTPROMO) Catalogs of Galactic
  Globular Clusters. V. The rapid rotation of 47 Tuc traced and modeled in
  three dimensions
  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 deg, 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 deg), 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/sigma 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.
