Structural properties of artificial halos in non-standard dark matter simulations

TL;DR

This paper investigates how artificial halos caused by simulation artifacts affect the properties of dark matter halos in non-standard models and proposes a method to identify and remove these spurious halos to improve the accuracy of simulation results.

Contribution

The study demonstrates that spurious halos have distinct properties and introduces a virial equilibrium-based criterion to effectively eliminate them from halo catalogs.

Findings

Spurious halos tend to have higher spin and elliptical shapes.

They significantly deviate from virial equilibrium.

Removing these halos restores the accuracy of the halo mass function.

Abstract

Artificial fragmentation of the matter density field causes the formation of spurious groups of particles in N-body simulations of non-standard Dark Matter (DM) models which are characterized by a small scale cut-off in the linear matter power spectrum. These spurious halos alter the prediction of the mass function in a range of masses where differences among DM models are most relevant to observational tests. Using a suite of high resolution simulations we show that the contamination of artificial groups of particles significantly affect the statistics of halo spin, shape and virial state parameters. We find that spurious halos have systematically larger spin values, are highly elliptical or prolate and significantly deviate from virial equilibrium. These characteristics allow us to detect the presence of spurious halos even in non-standard DM models for which the low-mass end of the mass function remains well behaved. We show that selecting halos near the virial equilibrium provides a simple and effective method to remove the bulk of spurious halos from numerical halo catalogs and consistently recover the halo mass function at low masses.