Sensitivity of Halo Shape Measurements

TL;DR

This paper investigates how the accuracy of halo shape measurements in cosmological simulations is influenced not only by resolution but also by density gradients, affecting measurements especially in halo centers.

Contribution

It introduces a criterion based on density gradients to assess the reliability of halo shape measurements in simulations, highlighting limitations in cored density profiles.

Findings

Shape measurement quality depends on density gradient, not just resolution.

Cored density profiles restrict reliable shape measurements.

The criterion helps identify regions where shape measurements are trustworthy.

Abstract

Shape measurements of galaxies and galaxy clusters are widespread in the analysis of cosmological simulations. But the limitations of those measurements have been poorly investigated. In this paper, we explain why the quality of the shape measurement does not only depend on the numerical resolution, but also on the density gradient. In particular, this can limit the quality of measurements in the central regions of haloes. We propose a criterion to estimate the sensitivity of the measured shapes based on the density gradient of the halo and to apply it to cosmological simulations of collisionless and self-interacting dark matter. By this, we demonstrate where reliable measurements of the halo shape are possible and how cored density profiles limit their applicability.