Discovery of rotation axis alignments in Milky Way globular clusters

A.E PIATTI

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2020 vol. 638 p. 12 - 15

0004-6361

There is an increasing number of recent observational results which show that some globular clusters exhibit internal rotation while they travel along their orbital trajectories around the Milky Way center. Based on these findings, we looked for any relationship between the inclination angles of the globular clusters? orbits with respect to the Milky Way plane and those of their rotation. We discovered that the relative inclination, in the sense rotation axis inclination − orbit axis inclination, is a function of the globular cluster?s orbit inclination. Rotation and orbit axes are aligned for an inclination of ∼ 56◦, while the rotation axis inclination is far from the orbit?s one between ∼ 20◦ and −20◦ when the latter increases from 0◦ up to 90◦. We further investigated the origin of such a linear relationship and found no correlation with the semimajor axes and eccentricities of the globular clusters? orbits, nor with the internal rotation strength, the globular clusters? sizes, actual and tidally disrupted masses, half-mass relaxation times, among others. The uncovered relationship will impact on the development of numerical simulations of the internal rotation of globular clusters, on our understanding about the interaction of the globular clusters with the Milky Way gravitational field, and on the observational campaigns for increasing the number of studied globular clusters with detected internal rotation.