Relation between halo spin and cosmic web filaments at z=3

TL;DR

This study uses cosmological simulations at high redshift to confirm and extend the understanding of how dark matter halo spins relate to the number and orientation of cosmic web filaments, supporting tidal torque theory.

Contribution

It demonstrates a mass-dependent and merger history-dependent relation between halo spin and filament connectivity, providing new insights into spin evolution in the cosmic web.

Findings

Halos with fewer filaments have larger spins.

The spin-filament relation is stronger for higher mass halos.

Larger spin halos have filaments more perpendicular to their spin vector.

Abstract

We investigate the spin evolution of dark matter haloes and their dependence on the number of connected filaments from the cosmic web at high redshift (spin-filament relation hereafter). To this purpose, we have simulated $5000$ haloes in the mass range $5\times10^{9}h^{-1}M_{\odot}$ to $5\times10^{11}h^{-1}M_{\odot}$ at $z=3$ in cosmological N-body simulations. We confirm the relation found by Prieto et al. 2015 where haloes with fewer filaments have larger spin. We also found that this relation is more significant for higher halo masses, and for haloes with a passive (no major mergers) assembly history. Another finding is that haloes with larger spin or with fewer filaments have their filaments more perpendicularly aligned with the spin vector. Our results point to a picture in which the initial spin of haloes is well described by tidal torque theory and then gets subsequently modified in a predictable way because of the topology of the cosmic web, which in turn is given by the currently favoured LCDM model. Our spin-filament relation is a prediction from LCDM that could be tested with observations.