Distinguishing Dark Matter Cusps from Cores using Globular Clusters

TL;DR

This study uses N-body simulations to show that the presence of nuclear star clusters in galaxies can indicate a cuspy dark matter halo, based on globular cluster dynamics and merger history.

Contribution

It demonstrates that globular cluster mergers and the formation of nuclear star clusters can distinguish between cuspy and cored dark matter halos in dwarf galaxies.

Findings

NSC formation occurs only in cuspy halos due to GC mergers.

GC mass functions and NSC presence can serve as indicators of halo cuspiness.

Dynamical friction stalling in cored halos prevents NSC formation.

Abstract

Globular Clusters (GCs) provide valuable insight into the properties of their host galaxies' dark matter halos. Using N-body simulations incorporating semianalytic dynamical friction and GC-GC merger prescriptions, we study the evolution of GC radial distributions and mass functions in cuspy and cored dark matter halos. Modeling the dynamics of the GC-rich system in the dwarf galaxy UGC 7369, we find that friction-induced inspiral and subsequent mergers of massive GCs can naturally and robustly explain the mass segregation of the GCs and the existence of a nuclear star cluster (NSC). However, the multiple mergers required to form the NSC only take place when the dark matter halo is cuspy. In a cored halo, stalling of the dynamical friction within the core halts the inspiral of the GCs, and so the GC merger rate falls significantly, precluding the formation of an NSC. We therefore argue that the presence of an NSC requires a cusp in UGC 7369. More generally, we propose that the presence of an NSC and the corresponding alteration of the GC mass function due to mergers may be used as an indicator of a cuspy halo for galaxies in which we expect NSC formation to be merger-dominated. These observables represent a simple, powerful complement to other inner halo density profile constraint techniques, and should allow for straightforward extension to larger samples.