On the shape of dark matter halos from MultiDark Planck simulations

TL;DR

This paper derives scaling relations for dark matter halo shapes across a wide mass range using MultiDark Planck simulations, revealing how halo ellipticity varies with mass and redshift, impacting observational properties.

Contribution

It provides new fitting functions for halo shape ratios as a function of mass and redshift based on large cosmological simulations, enhancing understanding of halo triaxiality.

Findings

Scaling relations for halo shapes over four orders of magnitude in mass.

Shape ratios depend on peak height, mass, and redshift.

Results inform lensing and observational studies of galaxy clusters.

Abstract

The halo shape plays a central role in determining important observational properties of the haloes such as mass, concentration and lensing cross-sections. The triaxiality of lensing galaxy clusters has a substantial impact on the distribution of the largest Einstein radii, while weak lensing techniques are sensitive to the intrinsic halo ellipticity. In this work, we provide scaling relations for the shapes of dark matter haloes as a function of mass (peak height) and redshift over more than four orders of magnitude in halo masses, namely from $10^{11.5}$ to $10^{15.8}~h^{-1}~$M$_\odot$. We have analysed four dark matter only simulations from the MultiDark cosmological simulation suite with more than 56 billion particles within boxes of 4.0, 2.5, 1.0 and 0.4 $h^{-1}$Gpc size assuming \textit{Planck} cosmology. The dark matter haloes have been identified in the simulations using the {\sc rockstar} halo finder, which also determines the axis ratios in terms of the diagonalization of the inertia tensor. In order to infer the shape for a hypothetical halo of a given mass at a given redshift, we provide fitting functions to the minor-to-major and intermediate-to-major axis ratios as a function of the peak height.