# Satellite Dwarf Galaxies in a Hierarchical Universe: The Prevalence of Dwarf-Dwarf Major Mergers

**Authors:** Alis Deason, Andrew Wetzel, Shea Garrison-Kimmel  
**arXiv:** [1406.3344](https://arxiv.org/abs/1406.3344)  
**Date:** 2014-06-12  
**Summary page:** https://www.summarizepaper.com/en/paper/1406.3344v1/

## Key points

- The study investigates the prevalence of major mergers between dwarf galaxies in the Local Group
- Mergers are well-known among massive galaxies and galaxy clusters, but their importance for dwarf galaxies in this group is poorly understood
- The authors utilize the ELVIS suite of cosmological simulations to explore this topic
- Approximately 10% of satellite dwarf galaxies with stellar masses greater than 10^6 times the mass of our Sun have experienced a major merger since z = 1
- Lower mass dwarf galaxies have a lower fraction of major mergers compared to more massive counterparts
- Recent merger remnants tend to be biased towards larger radial distances from their host halo and more recent virial infall times
- Satellite-satellite mergers can occur within the host halo after virial infall, facilitated by a significant proportion of dwarf galaxies falling into their host halo as part of a group
- Dwarf galaxies located outside of their host's virial radius have double the merger fraction compared to those within it
- Observable remnants from dwarf mergers can provide insights into star formation histories and gas content involved in such mergers
- The presence of massive black holes within dwarf galaxies and how mergers may influence their formation is explored

## Summary

In this study, the authors investigate the prevalence of major mergers between dwarf galaxies in the Local Group, which is a collection of galaxies that includes the Milky Way and Andromeda galaxies. While mergers are well-known to occur frequently among massive galaxies and galaxy clusters, their importance for dwarf galaxies in this group remains poorly understood. To explore this topic, the authors utilize the ELVIS suite of cosmological simulations, which are dissipationless simulations that focus on Milky Way- and Andromeda-like host halos. They specifically examine satellite dwarf galaxies with stellar masses greater than 10^6 times the mass of our Sun that are located within the virial radius of their respective host halos. The results reveal that approximately 10% of these satellite dwarf galaxies have experienced a major merger since z = 1 (a redshift corresponding to about half the age of the universe). A major merger is defined as one where the ratio of stellar masses between merging dwarfs is closer than 0.1. However, it should be noted that lower mass dwarf galaxies have a lower fraction of major mergers compared to their more massive counterparts. The analysis also shows that recent merger remnants tend to be biased towards larger radial distances from their host halo and more recent virial infall times. This bias arises because most recent mergers occurred shortly before crossing within the virial radius of their host halo. Additionally, satellite-satellite mergers can occur within the host halo after virial infall, facilitated by a significant proportion of dwarf galaxies falling into their host halo as part of a group. Interestingly, when considering dwarf galaxies located outside of their host's virial radius, the merger fraction doubles compared to those within it. This suggests that the most distant dwarf galaxies in the Local Group are more likely to have experienced a recent major merger event. The authors discuss several implications arising from these findings. They consider how observable remnants from dwarf mergers can provide insights into star formation histories and gas content involved in such mergers. Additionally, they explore potential presence of massive black holes within dwarf galaxies and how mergers may influence their formation. Overall, this study sheds light on prevalence of major mergers among dwarf galaxies in Local Group providing valuable information for understanding hierarchical structure formation process in this cosmological context.