Correlations between triaxial shapes and formation history of dark matter haloes

The shape of dark matter (DM) 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 DM 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 normalized peak-centroid offset. These correlations are 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 multidimensional 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-sized haloes. Our model should be useful for exploring the impact of triaxial halo shape on cosmological constraints in upcoming weak lensing surveys of galaxy clusters.

Automated summary

This study explores the correlations between the triaxial shapes and formation histories of dark matter haloes, revealing a strong correlation between halo ellipticity and properties indicative of halo formation history. These correlations remain largely unchanged regardless of halo density peak height. A simple model is proposed for the correlation between halo ellipticity and concentration, providing fitting formulae for the multidimensional distribution of triaxial halo shapes based on halo peak height. The halo shape model is applied to assess the impact of halo ellipticity and orientation bias on excess surface mass density profiles in cluster-sized haloes, and may be useful for understanding the influence of triaxial halo shape on cosmological constraints in upcoming weak lensing surveys of galaxy clusters.