On the Evolution of Dark Matter Halo Properties Following Major and Minor Mergers

TL;DR

This study analyzes dark matter halo evolution after major and minor mergers using simulation data, revealing the significant role of minor mergers in halo relaxation and galaxy formation.

Contribution

Introduces a novel merger detection algorithm based on property peaks, highlighting the importance of minor mergers in halo evolution.

Findings

Minor mergers cause relaxation similar to major mergers.

A new algorithm effectively detects minor mergers.

Minor mergers significantly influence galaxy formation models.

Abstract

We conducted an analysis on dark matter halo properties following major and minor mergers to advance our understanding of halo evolution. In this work, we analyzed ~80,000 dark matter halos from the Bolshoi-Planck cosmological simulation and studied halo evolution during relaxation after major mergers, those in which the merging mass ratio m/M > 0.3. We then applied a Gaussian filter to the property evolutions and characterized peak distributions, frequencies, and variabilities for several halo properties, including centering, spin, shape (prolateness), scale radius, and virial ratio. However, there were also halos that experienced relaxation without the presence of major mergers. We hypothesized that this was due to minor mergers unrecorded by the simulation analysis. By using property peaks to create a novel merger detection algorithm, we attempted to find minor mergers and match them to the unaccounted relaxed halos. Not only did we find evidence that minor mergers were the causes, but we also found similarities between major and minor merger effects, showing the significance of minor mergers for future studies. Through our dark matter merger statistics, we expect our work to ultimately serve as vital parameters towards better understanding galaxy formation and evolution.