Distinguishing Dark Matter Cusps from Cores using Globular Clusters

Shaunak Modak, Shany Danieli, Jenny E. Greene

Submitted on 2 November 2022


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 UGC7369, 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 UGC7369. 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.


Comment: 19 pages, 11 figures. Main results in figures 7 and 8. Submitted to ApJ, comments are welcome!

Subject: Astrophysics - Astrophysics of Galaxies


The stellar masses and total mass in GCs of the galaxies in the \citet{Georgiev_sample3} sample, color-coded by the number of GCs present in the system. UGC\,7369, circled in purple, is visible as a clear outlier compared to the remainder of the sample in $N_{GC}$. For comparison, the red star shows the position of NGC\,5846-UDG1 (studied in \citealt{UDG1_GCs, UDG1_DF}), which has an even higher $N_{GC}=33$, in this plane.