The Impact of Cluster Structure and Dynamical State on Scatter in the Sunyaev-Zel'dovich Flux-Mass Relation

TL;DR

This study investigates the intrinsic scatter in the Sunyaev-Zel'dovich flux-mass relation of galaxy clusters, revealing non-normal distribution features and identifying key factors like halo concentration that influence scatter, with implications for cosmological measurements.

Contribution

The paper provides a detailed analysis of the physical origins of scatter in the SZ flux-mass relation, highlighting the importance of higher-order moments and the role of halo concentration in reducing scatter.

Findings

Scatter exhibits positive skewness and kurtosis, deviating from lognormal assumptions.

Halo concentration strongly correlates with scatter, enabling significant reduction.

Cross-calibration with X-ray data can further decrease scatter and identify outliers.

Abstract

Cosmological constraints from cluster surveys rely on accurate mass estimates from the mass-observable relations. In order to avoid systematic biases and reduce uncertainties, we study the form and physical origin of the intrinsic scatter about the mean Sunyaev-Zel'dovich (SZ) flux-mass relation using a hydrodynamical simulation of galaxy cluster formation. We examine the assumption of lognormal scatter and detect non-negligible positive skewness and kurtosis (> 0.5) for a wide range of limiting masses and redshifts. These higher-order moments should be included in the parametrization of scatter in order not to bias cosmological constraints. We investigate the sources of the scatter by correlating it with measures of cluster morphology, halo concentration, and dynamical state, and we quantify the individual contribution from each source. We find that statistically the impact of dynamical state is weak, so the selection bias due to mergers is negligible. On the other hand, there is a strong correlation between the scatter and halo concentration, which can be used to reduce the scatter significantly (from 12.07% to 7.34% or by ~40% for clusters at z = 0). We also show that a cross-calibration by combining information from X-ray followups can be used to reduce the scatter in the flux-mass relation and also identify outliers in both X-ray and SZ cluster surveys.