COULD GLOBULAR CLUSTERS IN THE VICINITY OF THE GALACTIC CENTRE HAVE CONTRIBUTED STARS TO THE NUCLEAR STAR CLUSTER IN THE PAST?

Abstract

The results of direct N-body simulations of three Milky Way bulge globular clusters – Terzan 2, Terzan 4, and Terzan 5 – evolving in a time-varying galactic potential derived from the IllustrisTNG-100 cosmological database over 8 Gyr are presented. Incorporating full stellar evolution and compact remnant formation, we quantify the probability and efficiency of stellar accretion onto the Galactic nuclear star cluster (NSC) during close pericentre passages of these three clusters. To parametrize the effect of dynamical friction in the dense central environment, we introduce a velocity reduction factor (Vred) ranging from 1.00 to 0.10. It was found that all three clusters contribute stars to the NSC even in the absence of velocity reduction, with a combined bound stellar count of ~730 stars and a total accreted mass of ~278 M☉ at Vred = 1.00, growing to ~5420 stars and ~1175 M☉ at Vred = 0.10. Terzan 4 is the dominant contributor across all velocity reduction factors, reflecting its more frequent and closer pericentre passages near the Galactic centre. The mass distribution of accreted stars reveals a bimodal structure: a low-mass component below ~1 M☉ whose capture is independent of Vred, and a prominent high-mass tail extending to ~20 M☉ corresponding to neutron stars and black holes, which grows with decreasing Vred. Notably, Terzan 4 is the only cluster for which white dwarfs are also captured by the NSC at every Vred value. Our results suggest that the Terzan family represents a more significant source of compact remnants for the Galactic NSC than previously studied clusters, while confirming that tidal stripping of surviving globular clusters alone cannot account for the total NSC mass.