Formation imprints in the kinematics of the Milky Way globular cluster system

ANDRÉS E. PIATTI

ASTROPHYSICAL JOURNAL

IOP PUBLISHING LTD

Lugar: Londres; Año: 2019 vol. 882 p. 1 - 6

0004-637X

We report results on the kinematics of Milky Way (MW) globular clusters (GCs)based on updated space velocities for nearly the entireGC population.  We found that a 3D space with the semi-major axis, the eccentricityand the inclination of the orbit with respect to the MW plane as its axes is helpful in order to dig into the formation of the GC system. We find that GCs formed {it in-situ} show a clear correlation between their eccentricities and their orbital inclinationin the sense that clusters with large eccentricities also have large inclinations.These GCs also show a correlation between their distance to the MW centerand their eccentricity. Accreted GCs  do not exhibit a relationship between eccentricity and inclination, but span a wide variety of inclinations at eccentricities larger than $sim$ 0.5. Finally, we computed the velocity anisotropy $eta$ of the GC system and found for GCs formed {it in-situ}that $eta$ decreases from $approx$ 0.8 down to 0.3 from the outermost regions towards the MWcenter, but remains fairly constant (0.7-0.9) for accreted ones.These findings can be explained if GCs formed from gas that collapsed radially in the outskirts, with preference for relative high infall angles. As the material reached the rotating forming disk, it became more circular andmoved with lower inclination relative to the disk. A half of the GC population was accreted and deposited in orbits covering the entire range of energies from the outer halo to the bulge.