The absolute proper motions of the Arches and Quintuplet clusters

TL;DR

This study transforms relative proper motions of the Arches and Quintuplet clusters into an absolute reference frame using Gaia DR2 data, providing new insights into their motions near the Galactic Center.

Contribution

First to convert the clusters' proper motions onto an absolute system, enabling better understanding of their dynamics and origins.

Findings

Measured absolute proper motions for both clusters.

Found clusters move nearly parallel to the Galactic plane.

Highlighted need for distance measurements to determine orbits.

Abstract

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.