Rotational Kinematics in the Globular Cluster System of M31: Insights from Bayesian Inference

As ancient stellar systems, globular clusters (GCs) offer valuable insights into the dynamical histories of large galaxies. Previous studies of GC populations in the inner and outer regions of the Andromeda Galaxy (M31) have revealed intriguing subpopulations with distinct kinematic properties. Here, we build upon earlier studies by employing Bayesian modelling to investigate the kinematics of the combined inner and outer GC populations of M31. Given the heterogeneous nature of the data, we {examine} subpopulations defined by {GCs’} metallicity and {by} associations with substructure, in order to characterise possible relationships between the inner and outer {GC} populations. We find that lower-metallicity GCs and those linked to substructures exhibit a common, more rapid rotation, whose alignment is distinct from that of higher-metallicity and non-substructure GCs. Furthermore, the higher-metallicity GCs rotate in alignment with Andromeda’s stellar disc. These pronounced kinematic differences reinforce the idea that different subgroups of {GCs} were accreted to M31 at distinct epochs, shedding light on the complex assembly history of the galaxy.