Correlations between Triaxial Shapes and Formation History of Dark Matter Haloes

TL;DR

This paper investigates the relationship between dark matter halo shapes and their formation histories using simulations, providing models to improve cosmological analyses in upcoming weak lensing surveys.

Contribution

It introduces a model linking halo ellipticity with formation history proxies and offers fitting formulas for triaxial halo shapes as functions of peak height.

Findings

Halo ellipticity correlates strongly with halo concentration and formation proxies.

The ellipticity-concentration correlation is nearly independent of peak height.

The model helps assess halo shape effects on weak lensing measurements.

Abstract

The shape of dark matter haloes plays a critical role in constraining cosmology with upcoming large-scale structure surveys. In this paper, we study the correlations between the triaxial shapes and formation histories in dark matter haloes in the MultiDark Planck 2 N-body cosmological simulation. We find that halo ellipticity is strongly correlated with halo properties that serve as proxies of halo formation history, such as halo concentration and the peak-centroid offset. In particular, the correlation between halo ellipticity and halo concentration is nearly independent of the halo density peak height. We present a simple model for the correlation between halo ellipticity and concentration using conditional abundance matching, and provide fitting formulae for the multi-dimensional distributions of triaxial halo shape as a function of halo peak height. We apply our halo shape model to gauge the effects of halo ellipticity and orientation bias on the excess surface mass density profiles in cluster-size halos. Our model should be useful for exploring the impact of triaxial halo shape on cosmological constraints in upcoming weak lensing surveys of galaxy clusters.