Wide‐Field Survey of Globular Clusters in M31. II. Kinematics of the Globular Cluster System

Abstract

We present a kinematic analysis of the globular cluster (GC) system in M31, using the velocity data for 504 GCs including those for 150 GCs in our wide-field survey. The all GC system shows strong rotation, with rotation amplitude of -->vrot ~ 190 km s−1, and weak rotation persists even for the outermost samples at -->| Y| ≥ 5 kpc, where Y represents the projected distance from the major axis. The rotation-corrected velocity dispersion for the GC system is estimated to be -->σp,r ~ 130 km s−1, and it increases from -->σp,r ~ 120 km s−1 at -->| Y| σp,r ~ 150 km s−1 at -->| Y| ≥ 5 kpc. These results are very similar to those for the metal-poor GCs. This shows that there is a dynamically hot halo in M31 that is rotating but primarily pressure-supported. We have identified 50 friendless GCs, and they appear to rotate around the major axis of M31. Both metal-rich GCs and metal-poor GCs show strong rotation in the inner region. The rotation for the faint GCs is stronger than that for the bright GCs. We have identified 56 GCs and GC candidates with X-ray detection including 39 GCs with measured velocities. The majority of X-ray-emitting GCs follow the disk rotation. We have derived a rotation curve of M31 using the GCs at -->| Y| ≤ 0.6 kpc. We have estimated the dynamical mass of M31 using Projected Mass Estimator (PME) and Tracer Mass Estimator (TME) as -->MPME = 5.5+ 0.4−0.3 × 1011 M☉ out to a radius of ~55 kpc and -->MTME = 19.2+ 1.4−1.3 × 1011 M☉ for a radius of ~100 kpc, respectively. We finally discuss the implication of these results and compare the kinematics of GCs with that of planetary nebulae in M31.