The Cosmic History of the Spin of Dark Matter Halos Within the Large-Scale Structure

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 halos at high redshift have a weak tendency to be orthogonal to filaments and high-mass halos have a stronger orthogonal alignment than low-mass halos. Since z = 1, the spins of low-mass halos have become weakly aligned parallel to filaments, whereas high-mass halos kept their orthogonal alignment. This recent parallel alignment of low-mass halos casts doubt on tidal torque theory as the sole mechanism for the buildup 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 halos only at very small separations, r < 0.3 Mpc h −1 , which is driven by substructure. A correlation of the spin parameter with halo mass is confirmed at high redshift.