Na-O anticorrelation and HB. IX. Kinematics of the program clusters. A link between systemic rotation and HB morphology?

TL;DR

This study investigates the internal kinematics of 20 globular clusters, exploring the relationship between systemic rotation, metallicity, and horizontal branch morphology, revealing significant correlations that suggest rotation influences cluster formation and stellar populations.

Contribution

It provides the first systematic analysis linking globular cluster kinematics, especially rotation, with multiple stellar populations and cluster properties, highlighting rotation's role in cluster formation.

Findings

No correlation between Na abundance and velocity dispersion or rotation.

Significant correlation between rotation-to-dispersion ratio and HB morphology.

Rotation correlates with metallicity, cluster luminosity, and velocity dispersion.

Abstract

We use accurate radial velocities for 1981 member stars in 20 Galactic globular clusters, collected within our large survey aimed at the analysis of the Na-O anti-correlation, to study the internal kinematics of the clusters. We performed the first systematic exploration of the possible connections between cluster kinematics and the multiple populations phenomenon in GCs. We did not find any significant correlation between Na abundance and either velocity dispersion or systemic rotation. We searched for systemic rotation in the eight clusters of our sample that lack such analysis from previous works in the literature (NGC2808, NGC5904, NGC6171, NGC6254, NGC6397, NGC6388, NGC6441, and NGC6838). These clusters are found to span a large range of rotational amplitudes, from ~0.0 km/s (NGC6397) to ~13.0 km/s (NGC6441). We found a significant correlation between the ratio of rotational velocity to central velocity dispersion (V_{rot}/sigma_0) and the Horizontal Branch Morphology parameter (B-R)/(B+R+V). V_{rot}/sigma_0 is found to correlate also with metallicity, possibly hinting to a significant role of dissipation in the process of formation of globular clusters. V_{rot} is found to correlate well with (B-R)/(B+R+V), M_V, sigma_0 and [Fe/H]. All these correlations strongly suggest that systemic rotation may be intimately linked with the processes that led to the formation of globular clusters and the stellar populations they host.