How our proto-nuclear star cluster formed and grew due to early globular cluster disruption. I. Case of low masses

TL;DR

This study uses detailed N-body simulations to explore how early globular cluster disruption contributed to the formation and growth of proto-nuclear star clusters in Milky Way-like galaxies, highlighting the limited mass contribution from this process.

Contribution

It provides the first detailed N-body simulation analysis of globular cluster disruption's role in early proto-NSC formation in Milky Way-like galaxies.

Findings

GCs with specific orbital eccentricities contribute most to proto-NSC mass

Accreted stars are predominantly low-mass (~0.33 Msun)

Globular cluster disruption accounts for about 6% of the current NSC mass

Abstract

We investigate the accretion of globular cluster stars on early cosmological timescales through detailed N-body simulations of theoretical GC models to assess the role of this mechanism in Milky Way-like galaxies. For the dynamical modelling, we used the updated parallel N-body code phi-GPU, including stellar evolution. We prepared three sets of GC models with different half-mass radii (r_hm), each consisting of 50 full N-body GC models, and integrated these models in an external, time-variable MW-like potential taken from the cosmological database IllustrisTNG-100. The simulations cover the time interval from -10 Gyr to -5 Gyr, enabling us to assess the rate of early stellar accretion onto the proto-NSC. We find that GC models with average orbital eccentricities of 0.4-0.5 and orbits oriented perpendicular to the galactic disc contribute most significantly to the mass of the proto-NSC formation. Accretion is especially efficient in the first billion years and in compact GC models with r_hm = 1 pc. In all sets, the dominant accreted stellar population consists of low-mass stars (~0.33 Msun). However, the accreted mass alone is insufficient to fully account for the current NSC mass. Based on our extended set of numerical simulations, we obtained an average lower limit of mass contribution (~6 percent) to the NSC from investigated GCs. The fraction of mass contribution from individual disrupted GCs can significantly vary from 0.1 percent up to 90 percent. Generally, we conclude that the GC stellar accretion channel alone might not be sufficient to ensure the present-day MW galaxy NSC mass budget.