The cosmic history of the spin of dark matter haloes within the large scale structure

TL;DR

This study uses N-body simulations to analyze the evolution and alignment of dark matter halo spins within large scale structures from redshift 3 to 1, revealing mass-dependent alignment trends and challenging existing theories.

Contribution

It provides new insights into the evolution of halo spin orientations and their dependence on mass and cosmic time, highlighting limitations of tidal torque theory.

Findings

High redshift halo spins are weakly orthogonal to filaments.

Low mass halo spins become parallel to filaments since z=1.

Strong spin alignment occurs only at very small separations (<0.3 Mpc/h).

Abstract

We use N-body simulations to investigate the evolution of the orientation and magnitude of dark matter halo angular momentum within the large scale structure since z=3. We look at the evolution of the alignment of halo spins with filaments and with each other, as well as the spin parameter, which is a measure of the magnitude of angular momentum. It was found that the angular momentum vectors of dark matter haloes at high redshift have a weak tendency to be orthogonal to filaments and high mass haloes have a stronger orthogonal alignment than low mass haloes. Since z=1, the spins of low mass haloes have become weakly aligned parallel to filaments, whereas high mass haloes kept their orthogonal alignment. This recent parallel alignment of low mass haloes casts doubt on tidal torque theory as the sole mechanism for the build up of angular momentum. We see evidence for bulk flows and the broadening of filaments over time in the alignments of halo spin and velocities. We find a significant alignment of the spin of neighboring dark matter haloes only at very small separations, $r<0.3$Mpc/h, which is driven by substructure. A correlation of the spin parameter with halo mass is confirmed at high redshift.