The ecology of dark matter haloes I: The rates and types of halo interactions

TL;DR

This paper investigates the frequency, types, and environmental dependence of dark matter halo interactions like mergers and flybys using cosmological simulations, revealing two distinct interaction modes and their evolution over cosmic time.

Contribution

It introduces a new empirical model for interaction rates based on halo mass, environment, and redshift, and identifies two different physical modes of halo interactions.

Findings

Most interactions occur in dense environments like groups and filaments.

Two modes of interactions are identified, suggesting different physical origins.

Satellite halos lose mass as they move deeper into host halos.

Abstract

Interactions such as mergers and flybys play a fundamental role in shaping galaxy morphology. Using the Horizon Run 4 cosmological N-body simulation, we studied the frequency and type of halo interactions, and their redshift evolution as a function of the environment defined by the large-scale density, pair separation, mass ratio, and target halo mass. Most interactions happen at large-scale density contrast $\delta \approx 20$, regardless of the redshift, corresponding to groups and relatively dense part of filaments. However, the fraction of interacting target is maximum at $\delta \approx 1000$. We provide a new empirical fitting form for the interaction rate as a function of the halo mass, large-scale density, and redshift. We also report the existence of two modes of interactions from the distributions of mass ratio and relative distance, implying two different physical origins of the interaction. Satellite targets lose their mass as they proceed deeper into the host halo. The relative importance of these two trends strongly depends on the large-scale density, target mass, and redshift.