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 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.
Original language | English |
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Article number | 167 |
Number of pages | 15 |
Journal | Astrophysical Journal |
Volume | 844 |
Issue number | 2 |
DOIs | |
Publication status | Published - 3 Aug 2017 |
Keywords / Materials (for Non-textual outputs)
- Astrophysics - Astrophysics of Galaxies
- Astrophysics - Instrumentation and Methods for Astrophysics
- Astrophysics - Solar and Stellar Astrophysics
- Galaxy: kinematics and dynamics
- globular clusters: individual (NGC 104) –
- proper motions
- stars: Population II