Non-Gaussian Scatter in Cluster Scaling Relations

TL;DR

This paper studies how non-Gaussian scatter, including skewness and kurtosis, in cluster mass-observable relations affects cluster counts and cosmological constraints, especially at high mass and redshift.

Contribution

It introduces a parameterization of non-Gaussian scatter in cluster scaling relations and analyzes its impact on cluster counts and dark energy constraints.

Findings

Higher order moments affect high scatter proxies at high redshift.

Non-Gaussianity introduces additional uncertainty in dark energy parameters.

Skewness influences the shape of the cluster mass function.

Abstract

We investigate the impact of non-Gaussian scatter in the cluster mass-observable scaling relation on the mass and redshift distribution of clusters detected by wide area surveys. We parameterize non-Gaussian scatter by incorporating the third and forth moments (skewness and kurtosis) into the distribution P(Mobs|M). We demonstrate that for low scatter mass proxies the higher order moments do not significantly affect the observed cluster mass and redshift distributions. However, for high scatter mass indicators it is necessary for the survey limiting mass threshold to be less than 10^14 h^-1 Msol to prevent the skewness from having a significant impact on the observed number counts, particularly at high redshift. We also show that an unknown level of non-Gaussianity in the scatter is equivalent to an additional uncertainty on the variance in P(Mobs|M) and thus may limit the constraints that can be placed on the dark energy equation of state parameter w. Furthermore, positive skewness flattens the mass function at the high mass end, and so one must also account for skewness in P(Mobs|M) when using the shape of the mass function to constrain cluster scaling-relations.