Voronoi Tessellation and Non-parametric Halo Concentration

TL;DR

TesseRACt is a new non-parametric method using Voronoi tessellation that accurately recovers dark matter halo concentrations in simulations, outperforming traditional spherical assumptions especially in non-spherical and substructured halos.

Contribution

The paper introduces TesseRACt, a non-parametric, Voronoi tessellation-based technique for measuring halo concentration, which is more accurate for realistic, non-spherical halos with substructure.

Findings

TesseRACt recovers halo concentrations within 0.3% of true values.

Traditional methods can be off by up to 10% for non-spherical halos.

TesseRACt performs better in halos with external substructure.

Abstract

We present and test TesseRACt, a non-parametric technique for recovering the concentration of simulated dark matter halos using Voronoi tessellation. TesseRACt is tested on idealized N-body halos that are axisymmetric, triaxial, and contain substructure and compared to traditional least-squares fitting as well as two non-parametric techniques that assume spherical symmetry. TesseRACt recovers halo concentrations within 0.3% of the true value regardless of whether the halo is spherical, axisymmetric, or triaxial. Traditional fitting and non-parametric techniques that assume spherical symmetry can return concentrations that are systematically off by as much as 10% from the true value for non-spherical halos. TesseRACt also performs significantly better when there is substructure present outside $0.5R_{200}$. Given that cosmological halos are rarely spherical and often contain substructure, we discuss implications for studies of halo concentration in cosmological N-body simulations including how choice of technique for measuring concentration might bias scaling relations.