Spatial and kinematic segregation in star cluster merger remnants

TL;DR

This study uses N-body simulations to investigate whether star cluster mergers can explain the observed substructure in nuclear star clusters, finding that recent mergers retain distinguishable kinematic features.

Contribution

The paper demonstrates that multiple star cluster mergers alone cannot fully account for the observed properties of nuclear star clusters, highlighting the need for in situ star formation.

Findings

Recent mergers retain distinguishable kinematics.

Number of mergers influences substructure persistence.

In situ star formation is necessary for observed properties.

Abstract

Globular clusters which exhibit chemical and dynamical complexity have been suggested to be the stripped nuclei of dwarf galaxies (e.g., M54, $\omega$ Cen). We use $N$-body simulations of nuclear star clusters forming via the mergers of star clusters to explore the persistence of substructure in the phase space. We find that the observed level of differentiation is difficult to reconcile with the observed if nuclear clusters form wholly out of the mergers of star clusters. Only the star clusters that merged most recently retain sufficiently distinct kinematics to be distinguishable from the rest of the nuclear cluster though the critical factor is the number of merger events not the elapsed time. In situ star formation must therefore be included to explain the observed properties of nuclear star clusters, in good agreement with previous results.