Triaxial vs. Spherical Dark Matter Halo Profiles

Abstract

When analysing dark matter halos forming in cosmological N-body simulations it is common practice to obtain the density profile utilizing spherical shells. However, it is also known that the systems under investigation are far from spherical symmetry and rather follow a triaxial mass distribution. In this study we present an estimator for the error introduced by spherically averaging an elliptical mass distribution. We systematically investigate the differences arising when using a triaxial density profile under the assumption of spherical symmetry. We show that the variance in the density can be as large as 50% in the outer parts of dark matter halos for extreme (but still credible) axis ratios of 0.55:0.67:1. The inner parts are less affected but still show a scatter at the 16% level for these prolate systems. For more moderate ellipticities, i.e. axis ratios of 0.73:0.87:1, the error is smaller but still as large as 10-20% depending on distance. We further provide a simple formula that allows to estimate this variance as a function of radius for arbitrary axis ratios. We conclude that highly prolate and/or oblate systems are better fit by analytical profiles that take into account the triaxial nature of cosmological objects.

4 pages. 3 figures, accepted for publication in PASA

References in corpus (26)

• A Universal Density Profile from Hierarchical Clustering
• Cold collapse and the core catastrophe
• The Inner Structure of LambdaCDM Halos III: Universality and Asymptotic Slopes
• The Inner Structure of LambdaCDM Halos I: A Numerical Convergence Study
• Resolving the Structure of Cold Dark Matter Halos
• Triaxial Modeling of Halo Density Profiles with High-resolution N-body Simulations
• The Shape of Dark Matter Halos: Dependence on Mass, Redshift, Radius, and Formation
• Density Profiles of Dark Matter Halo are not Universal
• The Central Mass Distribution in Dwarf and Low Surface Brightness Galaxies
• Internal and External Alignment of the Shapes and Angular Momenta of LCDM Halos
• High-Resolution Measurements of the Halos of Four Dark Matter-Dominated Galaxies: Deviations from a Universal Density Profile
• The Effect of Gas Cooling on the Shapes of Dark Matter Halos
• The Phase-Space Density Profiles of Cold Dark Matter Halos
• The density profile of equilibrium and non-equilibrium dark matter halos
• On the Origin of Cusps in Dark Matter Halos
• Convergence and scatter of cluster density profiles
• Structure of Dark Matter Halos From Hierarchical Clustering
• Cusps in CDM halos
• Shapes and Alignments of Galaxy Cluster Halos
• Dynamical insight into dark-matter haloes
• Internal Alignment of the Halos of Disk Galaxies in Cosmological Hydrodynamic Simulations
• Can the Steep Mass Profile of A1689 Be Explained by a Triaxial Dark Halo?
• Density profiles of LCDM clusters
• Structure of Dark Matter Halos From Hierarchical Clustering. III. Shallowing of The Inner Cusp
• Semi-analytical dark matter halos and the Jeans equation
• Dark matter density profiles from the Jeans equation

Cited by in corpus (12)

• Cosmic Ménage à Trois: The Origin of Satellite Galaxies On Extreme Orbits
• The Graininess of Dark Matter Haloes
• Extrinsic Sources of Scatter in the Richness-Mass Relation of Galaxy Clusters
• A cuspy dark matter halo
• Systematic Problems With Using Dark Matter Simulations to Model Stellar Halos
• Alas, the dark matter structures were not that trivial
• Systematic uncertainties from halo asphericity in dark matter searches
• The massive dark halo of the compact, early-type galaxy NGC 1281
• On the choice of the most suitable indicator for the assembly state of dark matter haloes through cosmic time
• Chameleon Screening Depends on the Shape and Structure of NFW Halos
• Three-dimensional shapelets and an automated classification scheme for dark matter haloes
• An analytical model of surface mass densities of cold dark matter haloes - with an application to MACHO microlensing optical depths