Star Clusters in M31: Old Clusters with Bar Kinematics

TL;DR

This study examines the kinematics of old star clusters in M31's inner regions, revealing evidence of a bar structure influencing their motions, with metal-rich clusters showing disk-like kinematics and metal-poor clusters indicating spheroid support.

Contribution

It provides detailed kinematic analysis of M31's old clusters, demonstrating the presence of bar-related orbital patterns in the inner galaxy regions.

Findings

Metal-poor clusters exhibit spheroid-like kinematics.

Metal-rich clusters show disk-like kinematics.

Inner 2 kpc region displays bar orbit signatures.

Abstract

We analyze our accurate kinematical data for the old clusters in the inner regions of M31. These velocities are based on high S/N Hectospec data (Caldwell et al 2010). The data are well suited for analysis of M31's inner regions because we took particular care to correct for contamination by unresolved field stars from the disk and bulge in the fibers. The metal poor clusters show kinematics which are compatible with a pressure-supported spheroid. The kinematics of metal-rich clusters, however, argue for a disk population. In particular the innermost region (inside 2 kpc) shows the kinematics of the x2 family of bar periodic orbits, arguing for the existence of an inner Lindblad resonance in M31.