Spin alignment of dark matter haloes in the shells of the largest voids

TL;DR

This study uses high-resolution simulations to analyze how dark matter haloes' orientations and angular momenta align with large cosmic voids, confirming and extending previous observational findings.

Contribution

First simulation-based measurement of the strength and radial dependence of halo alignment with voids, including baryonic matter, and its correlation with halo mass.

Findings

Haloes on void shells have angular momentum perpendicular to the void-centre direction.

Alignment strength decreases with distance from the void centre.

Stronger alignment observed in baryonic matter within haloes.

Abstract

Using the high resolution cosmological N-body simulation MareNostrum Universe we study the orientation of shape and angular momentum of galaxy-size dark matter haloes around large voids. We find that haloes located on the shells of the largest cosmic voids have angular momenta that tend to be preferentially perpendicular to the direction that joins the centre of the halo and the centre of the void. This alignment has been found in spiral galaxies around voids using galaxy redshift surveys. We measure for the first time the strength of this alignment, showing how it falls off with increasing distance to the centre of the void. We also confirm the correlation between the intensity of this alignment and the halo mass. The analysis of the orientation of the halo main axes confirms the results of previous works. Moreover, we find a similar alignment for the baryonic matter inside dark matter haloes, which is much stronger in their inner parts.