Stochastic Model of the Spin Distribution of Dark Matter Halos

Abstract

We employ a stochastic approach to probing the origin of the log-normal distributions of halo spin in N-body simulations. After analyzing spin evolution in halo merging trees, it was found that a spin change can be characterized by a stochastic random walk of angular momentum. Also, spin distributions generated by random walks are fairly consistent with those directly obtained from N-body simulations. We derived a stochastic differential equation from a widely used spin definition and measured the probability distributions of the derived angular momentum change from a massive set of halo merging trees. The roles of major merging and accretion are also statistically analyzed in evolving spin distributions. Several factors (local environment, halo mass, merging mass ratio, and redshift) are found to influence the angular momentum change. The spin distributions generated in the mean-field or void regions tend to shift slightly to a higher spin value compared with simulated spin distributions, which seems to be caused by the correlated random walks. We verified the assumption of randomness in the angular momentum change observed in the N-body simulation and detected several degrees of correlation between walks, which may provide a clue for the discrepancies between the simulated and generated spin distributions in the voids. However, the generated spin distributions in the group and cluster regions successfully match the simulated spin distribution. We also demonstrated that the log-normality of the spin distribution is a natural consequence of the stochastic differential equation of the halo spin, which is well described by the Geometric Brownian Motion model.

21 pages, 31 figures, Accepted for publication in ApJS

References in corpus (12)

• Properties of Dark Matter Haloes in Clusters, Filaments, Sheets and Voids
• The spin and shape of dark matter haloes in the Millennium simulation of a LambdaCDM universe
• Generating Dark Matter Halo Merger Trees
• N-body Dark Matter Haloes with simple Hierarchical Histories
• The spin and orientation of dark matter halos within cosmic filaments
• Constructing Merger Trees that Mimic N-Body Simulations
• The Alignments of the Galaxy Spins with the Real-Space Tidal Field Reconstructed from the Two Mass Redshift Survey
• Generating Merger Trees for Dark Matter Haloes: A Comparison of Methods
• Do Mergers Spin up Dark Matter Halos?
• On the Correlation between Spin Parameter and Halo Mass
• Environment and mass dependencies of galactic $\lambda$ spin parameter: cosmological simulations and observed galaxies compared
• Merger history trees of dark matter haloes in moving barrier models

Cited by in corpus (3)

• Ultra-diffuse galaxies: the high-spin tail of the abundant dwarf galaxy population
• High Angular Momentum Halo Gas: a Feedback and Code-Independent Prediction of LCDM
• Gas Accretion and Angular Momentum