Origin of rotational kinematics in the globular cluster system of M31: a new clue to the bulge formation

Abstract

Abstract We propose that the rotational kinematics of the globular cluster system (GCS) in M31 can result from a past major merger event that could have formed its bulge component. We numerically investigate kinematical properties of globular clusters (GCs) in remnants of galaxy mergers between two discs with GCs in both their disc and halo components. We find that the GCS formed during major merging can show strongly rotational kinematics with the maximum rotational velocities of ∼140–170 km s−1 for a certain range of orbital parameters of merging. We also find that a rotating stellar bar, which can be morphologically identified as a boxy bulge if seen edge-on, can be formed in models for which the GCSs show strongly rotational kinematics. We thus suggest that the observed rotational kinematics of GCs with different metallicities in M31 can be closely associated with the ancient major merger event. We discuss whether the formation of the rotating bulge/bar in M31 can be due to the ancient merger.