Sensitivity of dark matter haloes to their accretion histories

TL;DR

This study introduces a novel quadratic genetic modification method to generate varied mass accretion histories for dark matter haloes, revealing how merger smoothness and order influence halo concentration, thus advancing understanding of galaxy formation sensitivity.

Contribution

The paper presents a new technique for creating controlled halo formation histories, enabling detailed analysis of how accretion patterns affect halo properties beyond population averages.

Findings

Smoother merger histories lead to lower halo concentrations.

Halo concentration depends on the order of mergers at fixed formation time.

The method allows targeted studies of individual halo responses to accretion variations.

Abstract

We apply our recently proposed "quadratic genetic modification" approach to generating and testing the effects of alternative mass accretion histories for a single $\Lambda$CDM halo. The goal of the technique is to construct different formation histories, varying the overall contribution of mergers to the fixed final mass. This enables targeted studies of galaxy and dark matter halo formation's sensitivity to the smoothness of mass accretion. Here, we focus on two dark matter haloes, each with four different mass accretion histories. We find that the concentration of both haloes systematically decreases as their merger history becomes smoother. This causal trend tracks the known correlation between formation time and concentration parameters in the overall halo population. At fixed formation time, we further establish that halo concentrations are sensitive to the order in which mergers happen. This ability to study an individual halo's response to variations in its history is highly complementary to traditional methods based on emergent correlations from an extended halo population.