The absolute proper motions of the Arches and Quintuplet clusters
  Arches and Quintuplet are two young, massive clusters projected near the
Galactic Center. To date, studies focused on understanding their origin have
been based on proper motions (PMs) derived in the clusters' reference frames
and required some assumptions about their 3D motion. In this paper, we combine
public PM catalogs of these clusters with the Gaia DR2 catalog and, for the
first time, transform the relative PMs of the Arches and Quintuplet clusters
onto an absolute reference system. We find that the absolute PM of the Arches
is $(\mu_\alpha \cos\delta,\mu_\delta)$ $=$ $(-1.45\ \pm\ 0.23,-2.68\ \pm\
0.14)$ mas yr$^{-1}$, and that of the Quintuplet is $(\mu_\alpha
\cos\delta,\mu_\delta)$ $=$ $(-1.19\ \pm\ 0.09,-2.66\ \pm \ 0.18)$ mas
yr$^{-1}$. These values suggest that these systems are moving almost parallel
to the Galactic plane. A measurement of the clusters' distances is still
required to meaningfully constrain the clusters' orbits and shed light on the
origin of the Arches and Quintuplet.
