Abstract

We report results on the kinematics of Milky Way globular clusters based on updated space velocities for nearly the entire globular cluster population. We found that a 3D space with the semi-major axis, the eccentricity and the inclination of the orbit with respect to the Milky Way plane as its axes is helpful in order to dig into the formation of the globular cluster system. We find that globular clusters formed in-situ show a clear correlation between their eccentricities and their orbital inclination in the sense that clusters with large eccentricities also have large inclinations. Accreted globular clusters do not exhibit a relationship between eccentricity and inclination, but span a wide variety of inclinations at eccentricities larger than 0.5. These findings can be interpreted as if globular clusters formed from gas that collapsed radially in the outskirts, with preference for relative high infall angles. As the material reached the rotating forming disc, it became more circular and moved with lower inclination relative to the disc. A half of the globular cluster population was accreted and deposited in orbits covering the entire range of energies from the outer halo to the bulge.