Redshift evolution of the dark matter haloes shapes

TL;DR

This study investigates how the shapes of Milky Way-like dark matter haloes evolve over cosmic time, revealing that they become more spherical as accretion modes shift from filamentary to isotropic, influenced by baryonic effects.

Contribution

It provides new insights into the redshift evolution of halo shapes and their relation to accretion modes and environment using hydrodynamical simulations.

Findings

Haloes are more triaxial at earlier times due to filamentary accretion.

Halo shapes become more spherical as they evolve towards isotropic accretion.

Baryons influence inner halo shapes, making them rounder.

Abstract

In this work, we aim at investigating the morphology evolution of Milky Way mass-like dark matter haloes selected from the CIELO and IllustrisTNG Projects. The connection between halo shapes and their environment has been studied in previous works at z=0 but their connection remains yet to be fully understood. We focus on the evolution across cosmic time of the halo shapes and the relation with the infalling material, using hydrodynamical simulations. Our findings show that haloes tend to be more triaxial at earlier times as a consequence of stronger accretion in the direction of the filaments. As the haloes evolve towards a dominant isotropic accretion mode and relaxation, their shape at 20 percent of the virial mass becomes more spherical. In agreement with previous results, baryons have an important effect within the inner regions of the haloes, driving them from triaxial to rounder shapes. We also find a correlation between the strength of the quadrupole infalling mode and the degree of ellipticity of the haloes: as the filament strength decreases steadily with redshift, the haloes became more spherical and less elliptical.