Milky Way Subsystems from Globular Clusters Kinematics Using Gaia DR2
  and HST Data
  We employ Gaia DR2 proper motions for 151 Milky Way globular clusters from
Vasiliev (2019) in tandem with distances and line-of-sight velocities to derive
their kinematical properties. To assign clusters to the Milky Way thick disk,
bulge, and halo we follow the approach of Posti et al. (2018) who distinguished
among different Galactic stellar components using stars's orbits. In
particular, we use the ratio $L_{z}/e$, the $Z$ projection of the angular
momentum to the eccentricity, as population tracer, which we complement with
chemical abundances extracted from the literature and Monte-Carlo simulations.
We find that 20 globular clusters belong to the bar/bulge of the Milky Way, 35
exhibit disk properties, and 96 are members of the halo. Moreover, we find that
halo globular clusters have close to zero rotational velocity with average
value $<\Theta>$ =1$\pm$ 4 km s$^{-1}$. On the other hand, the sample of
clusters that belong to the thick disk possesses a significant rotation with
average rotational velocity 179 $\pm$ 6 km s$^{-1}$. The twenty globular
clusters orbiting within the bar/bulge region of the Milky Way galaxy have
average rotational velocity of 49 $\pm$ 11 km s$^{-1}$.
