Effect of Neutrinos on Angular Momentum of Dark Matter Halo

TL;DR

This study investigates how massive neutrinos influence the angular momentum and mass of dark matter halos using cosmological simulations, revealing significant reductions in halo properties and regional variations.

Contribution

It provides the first detailed statistical analysis of neutrino effects on dark matter halo angular momentum and mass in cosmological simulations.

Findings

Over 89.71% of halos have smaller moduli with neutrinos.

Most halos (86.60%) have lower masses with neutrinos.

Angular momentum orientations change less than 0.65° in most cases.

Abstract

Massive neutrinos are expected to affect the large-scale structure formation, including the major component of solid substances, dark matter halos. How halos are influenced by neutrinos is vital and interesting, and angular momentum (AM) as a significant feature provides a statistical perspective for this issue. Exploring halos from TianNu N-body cosmological simulation with the co-evolving neutrino particles, we obtain some concrete conclusions. First, by comparing the same halos with and without neutrinos, in contrast to the neutrino-free case, over 89.71\% of halos have smaller halo moduli, over 71.06\% have smaller particle-mass-reduced (PMR) AM moduli, and over 95.44\% change their orientations of less than $0.65^\circ$. Moreover, the relative variation of PMR modulus is more visible for low-mass halos. Second, to explore the PMR moduli of halos in dense or sparse areas, we divide the whole box into big cubes, and search for halos within a small spherical cell in a single cube. From the two-level divisions, we discover that in denser cubes, the variation of PMR moduli with massive neutrinos decreases more significantly. This distinction suggests that neutrinos exert heavier influence on halos' moduli in compact regions. With massive neutrinos, most halos (86.60\%) have lower masses than without neutrinos.