On the spin distributions of $\Lambda$CDM haloes

TL;DR

This paper investigates the distribution and evolution of the spin parameter in dark matter haloes using merger trees from extended Press-Schechter theory, revealing dependencies on halo mass, merger history, and redshift.

Contribution

It introduces a new analytical formula for the spin parameter distribution that better fits simulation data, and explores its dependence on halo properties and merger history.

Findings

Spin parameter increases with halo mass.

Distribution approximates a log-normal but with tail discrepancies.

Spin depends weakly on redshift and increases with recent major mergers.

Abstract

We used merger trees realizations, predicted by the extended Press-Schechter theory, in order to study the growth of angular momentum of dark matter haloes. Our results showed that: 1) The spin parameter $\lambda'$ resulting from the above method, is an increasing function of the present day mass of the halo. The mean value of $\lambda'$ varies from 0.0343 to 0.0484 for haloes with present day masses in the range of $ 10^9\mathrm{h}^{-1}M_{\odot}$ to $10^{14}\mathrm{h}^{-1}M_{\odot}$. 2)The distribution of $\lambda'$ is close to a log-normal, but, as it is already found in the results of N-body simulations, the match is not satisfactory at the tails of the distribution. A new analytical formula that approximates the results much more satisfactorily is presented. 3) The distribution of the values of $\lambda'$ depends only weakly on the redshift. 4) The spin parameter of an halo depends on the number of recent major mergers. Specifically the spin parameter is an increasing function of this number.