The young massive star cluster Westerlund 2 observed with MUSE. III. A
  cluster in motion -- the complex internal dynamics
  Analyzing the dynamical state of nearby young massive star clusters is
essential understanding star cluster formation and evolution during their
earliest stages. In this work we analyze the stellar and gas kinematics of the
young massive star cluster Westerlund 2 (Wd2) using data from the integral
field unit MUSE and complement them with proper motions from the Gaia DR2. The
mean gas radial velocity of $15.9\,{\rm km}\,{\rm s}^{-1}$ agrees with the
assumption that Wd2 is the result of a cloud-cloud collision. The gas motions
show the expansion of the HII region, driven by the radiation from the many OB
stars in the cluster center. The velocity profile of the cluster member stars
reveal an increasing velocity dispersion with decreasing stellar mass and that
the low-mass stars show five distinct velocity groups. Based on their spatial
correlation with the cluster's two clumps, we concluded that this is the
imprint of the initial cloud collapse that formed Wd2. A thorough analysis of
the dynamical state of Wd2, which determines a dynamical mass range of $M_{\rm
dyn,Wd2} = (7.5 \pm 1.9)\cdot10^4 - (4.4 \pm 1.1)\cdot10^5\,{\rm M}_\odot$ and
exceeds the photometric mass by at least a factor of two leads to the
conclusion that Wd2 is not massive enough to remain gravitationally bound.
Additionally we also identify 22 runaway candidates with peculiar velocities
between 30 and $546\,{\rm km}\,{\rm s}^{-1}$.
