Multiple populations in globular clusters: constraints from kinematics and dynamics

TL;DR

This paper examines how the kinematic and spatial properties of multiple stellar populations in globular clusters can inform their formation scenarios, emphasizing the potential of differential rotation as a key discriminant.

Contribution

It highlights the role of kinematic and spatial constraints, especially differential rotation, in understanding the formation of multiple populations in globular clusters.

Findings

Outer populations are more centrally concentrated, consistent with enrichment scenarios.

Differential rotation between subpopulations could distinguish formation models.

Mass segregation may be influenced by differences in binary fractions.

Abstract

We discuss constraints on the formation of multiple populations in globular clusters (GCs) imposed by their present-day kinematics (velocity dispersion and anisotropy) and spatial distribution. We argue that the observational evidence collected so far in the outer parts of clusters is generally consistent with an enriched population forming more centrally concentrated compared to the primordial population, in agreement with all the scenarios proposed to date (in some cases by design), but not sufficient to favour a particular scenario. We highlight that the differential rotation of subpopulations is a signature that may provide crucial new constraints and allow us to distinguish between various scenarios. Finally, we discuss the spatial distribution of subpopulations in the central regions of GCs and speculate that mass segregation between subpopulations may be due to a difference in their binary fraction.