The impact of filamentary accretion of subhaloes on the shape and orientation of haloes

TL;DR

This study uses high-resolution cosmological simulations to analyze how filamentary subhalo accretion influences the shape and orientation of dark matter haloes, revealing weak correlations and mass-dependent alignment effects.

Contribution

It is the first to quantify the correlation between halo shape/orientation and filamentary accretion strength across different halo masses.

Findings

Halo shape correlates weakly with filamentary accretion strength.

Highly anisotropic accretion leads to more spherical or oblate haloes.

Major axes align with filaments, but angular momentum vectors are slightly misaligned.

Abstract

Dark matter haloes are formed through hierarchical mergers of smaller haloes in large-scale cosmic environments, and thus anisotropic subhalo accretion through cosmic filaments have some impacts on halo structures. Recent studies using cosmological simulations have shown that the orientations of haloes correlate with the direction of cosmic filaments, and these correlations significantly depend on the halo mass. Using high-resolution cosmological $N$-body simulations, we quantified the strength of filamentary subhalo accretion for galaxy- and group-sized host haloes ($M_{\rm host}=5\times10^{11-13}M_{\odot}$) by regarding the entry points of subhaloes as filaments and present statistical studies that how the shape and orientation of host haloes at redshift zero correlate with the strength of filamentary subhalo accretion. We confirm previous studies that found the host halo mass dependence of the alignment between orientations of haloes and filaments. We also show that, for the first time, the shape and orientation of haloes weakly correlate with the strength of filamentary subhalo accretion even if the host halo masses are the same. Minor-to-major axis ratios of haloes tend to decrease as their filamentary accretion gets stronger. Haloes with highly anisotropic accretion become more spherical or oblate, while haloes with isotropic accretion become more prolate or triaxial. For haloes with strong filamentary accretion, their major axes are preferentially aligned with the filaments, while their angular momentum vectors tend to be slightly more misaligned.