Intrinsic scatter of caustic masses and hydrostatic bias: An observational study

Abstract

All estimates of cluster mass have some intrinsic scatter and perhaps some bias with true mass even in the absence of measurement errors for example caused by cluster triaxiality and large scale structure. Knowledge of the bias and scatter values is fundamental for both cluster cosmology and astrophysics. In this paper we show that the intrinsic scatter of a mass proxy can be constrained by measurements of the gas fraction because masses with higher values of intrinsic scatter with true mass produce more scattered gas fractions. Moreover, the relative bias of two mass estimates can be constrained by comparing the mean gas fraction at the same (nominal) cluster mass. Our observational study addresses the scatter between caustic (i.e., dynamically estimated) and true masses, and the relative bias of caustic and hydrostatic masses. For these purposes, we used the X-ray Unbiased Cluster Sample, a cluster sample selected independently from the intracluster medium content with reliable masses: 34 galaxy clusters in the nearby ($0.050<z<0.135$) Universe, mostly with $14<\log M_{500}/M_{\odot }\lesssim 14.5$, and with caustic masses. We found a 35\% scatter between caustic and true masses. Furthermore, we found that the relative bias between caustic and hydrostatic masses is small, $0.06\pm 0.05$ dex, improving upon past measurements. The small scatter found confirms our previous measurements of a highly variable amount of feedback from cluster to cluster, which is the cause of the observed large variety of core-excised X-ray luminosities and gas masses.

A&A, in press, minor language changes from previous version

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• An IllustrisTNG View of the Caustic Technique for Galaxy Cluster Mass Estimation
• Scaling relations of X-ray Luminous Clusters in the Hyper Suprime-Cam Subaru Strategic Program Field
• Cosmic accretion shocks as a tool to measure the dark matter mass of galaxy clusters
• Caustic and hydrostatic mass bias: Implications for modified gravity
• The uncommon intracluster medium features of the first massive clusters selected independently of their baryon content
• Where do X-ray low surface brightness clusters sit with respect to filaments?
• The eROSITA Final Equatorial-Depth Survey (eFEDS): X-ray stacking analysis of Subaru's optically selected clusters spanning low richness regime
• Hydrostatic equilibrium of X-ray gas in X-COP clusters with HMG