3D core kinematics of NGC$~$6362: central rotation in a dynamically evolved globular cluster

TL;DR

This study reveals the first detection of significant central rotation in the globular cluster NGC 6362, showing complex chemo-dynamical behavior and supporting theories of dynamical evolution and mass loss.

Contribution

It provides the first evidence of central line-of-sight rotation in NGC 6362 using combined spectroscopic and proper motion data, highlighting differential rotation among multiple populations.

Findings

Detected a central rotation signal of ~1 km/s in NGC 6362.

Na-rich stars rotate faster than Na-poor stars.

Rotation amplitude and position align with dynamical evolution models.

Abstract

We present a detailed 3D kinematic analysis of the central regions ($R<30''$) of the low-mass and dynamically evolved galactic globular cluster NGC 6362. The study is based on data obtained with ESO-VLT/MUSE used in combination with the adaptive optics module and providing $\sim3000$ line-of-sight radial velocities, which have been complemented with Hubble Space Telescope proper motions. The quality of the data and the number of available radial velocities allowed us to detect for the first time a significant rotation signal along the line of sight in the cluster core with amplitude of $\sim 1$ km/s and with a peak located at only $\sim20''$ from the cluster center, corresponding to only $\sim10\%$ of the cluster half-light radius. This result is further supported by the detection of a central and significant tangential anisotropy in the cluster innermost regions. This is one of the most central rotation signals ever observed in a globular cluster to date. We also explore the rotational properties of the multiple populations hosted by this cluster and find that Na-rich stars rotate about two times more rapidly than the Na-poor sub-population thus suggesting that the interpretation of the present-day globular cluster properties require a multi-component chemo-dynamical approach. Both the rotation amplitude and peak position would fit qualitatively the theoretical expectations for a system that lost a significant fraction of its original mass because of the long-term dynamical evolution and interaction with the Galaxy. However, to match the observations more quantitatively further theoretical studies to explore the initial dynamical properties of the cluster are needed.