# EDGE: A new model for Nuclear Star Cluster formation in dwarf galaxies

**Authors:** Emily I. Gray, Justin I. Read, Ethan Taylor, Matthew D. A. Orkney, Martin P. Rey, Robert M. Yates, Stacy Y. Kim, Noelia E. D. Noël, Oscar Agertz, Eric Andersson, Andrew Pontzen  
**arXiv:** [2405.19286](https://arxiv.org/abs/2405.19286)  
**Date:** 2024-05-29  
**Summary page:** https://www.summarizepaper.com/en/paper/2405.19286v1/

## Key points

- Nuclear Star Clusters (NSCs) are dense stellar systems found at the centers of many galaxies, including bright spiral and elliptical galaxies, as well as up to 40% of dwarf galaxies.
- A new formation mechanism for NSCs is proposed based on research findings from EDGE simulations focusing on isolated dwarf galaxies.
- NSCs naturally emerge in a subset of EDGE dwarfs with redshift-zero halo masses around $5 \times 10^9$ solar masses.
- The formation mechanism involves quenched dwarf galaxies experiencing a major merger event triggering rapid gas cooling and leading to a substantial starburst phase where an NSC forms and suppresses further star formation.
- NSCs formed in this manner from low mass host dwarf galaxies may potentially accrete onto galaxies across various mass ranges, playing a crucial role in seeding their formation throughout the universe.
- The model predicts that NSCs should exhibit at least two distinct stellar populations with a significant age gap exceeding one billion years, aligning with observations showing two main sequence turnoffs in color magnitude diagrams for nucleated dwarfs.
- Several GCs orbiting our Milky Way galaxy may actually be accreted NSCs based on their observed behavior matching the predicted characteristics from this study.

## Summary

Nuclear Star Clusters (NSCs) are dense stellar systems found at the centers of many galaxies, including bright spiral and elliptical galaxies, as well as up to 40% of dwarf galaxies. These compact structures have long been a topic of debate in the scientific community due to their potential links to globular clusters (GCs). In this study, conducted using the EDGE simulations - a series of zoom-in cosmological simulations focusing on isolated dwarf galaxies - a new formation mechanism for NSCs is proposed. The research findings indicate that NSCs naturally emerge in a subset of EDGE dwarfs with redshift-zero halo masses around $5 \times 10^9$ solar masses. These dwarf galaxies were quenched by reionization but retained a significant reservoir of gas that could not cool and form stars. Subsequently, these dwarfs experienced a major merger event with an approximate 1:1 ratio, triggering rapid gas cooling and leading to a substantial starburst. It is within this starburst phase that an NSC forms and subsequently suppresses further star formation in the galaxy. One unique aspect of this proposed mechanism is the low mass of the host dwarf galaxy, allowing NSCs formed in this manner to potentially accrete onto galaxies across various mass ranges. This suggests that NSCs may play a crucial role in seeding their formation throughout the universe. Additionally, the model predicts that NSCs should exhibit at least two distinct stellar populations with a significant age gap exceeding one billion years. This prediction aligns with observations showing two main sequence turnoffs in color magnitude diagrams for nucleated dwarfs. Furthermore, it is suggested that several GCs orbiting our Milky Way galaxy, such as Omega Centauri and M54, may actually be accreted NSCs based on their observed behavior matching the predicted characteristics from this study. Overall, these findings shed light on a novel mechanism for NSC formation in dwarf galaxies and provide insights into their potential role in seeding NSC formation across different galactic environments.