Galaxy Cluster Shapes and Systematic Errors in H 0 Measured by the Sunyaev‐Zeldovich Effect

Abstract

Imaging of the Sunyaev-Zeldovich (SZ) e ect in galaxy clusters combined with cluster plasma X-ray diagnostics can measure the cosmic distance scale to high redshift. However, projecting the inverse Compton scattering and X-ray emission along the cluster line of sight introduces systematic errors in the Hubble constant, because the true shape of the cluster is not known. In this paper, I present a study H 0 , of the systematic errors in the value of as determined by the X-ray and SZ properties of theoretical H 0 , samples of triaxial isothermal " " beta ÏÏ model clusters, caused by projection e ects and observer orienta-tion relative to the model clustersÏ principal axes. I calculate three estimates for for each cluster H 0 based on their large and small apparent angular core radii and their arithmetic mean. I demonstrate that the estimates for for a sample of 25 clusters have limited systematic error : the 99.7% conÐdence H 0 intervals for the mean estimated analyzing the clusters using either their large or mean angular core H 0 radius are within ^14% of the " " true ÏÏ (assumed) value of (and enclose it), for a triaxial beta model H 0 cluster sample possessing a distribution of apparent X-ray cluster ellipticities consistent with that of observed X-ray clusters. This limit on the systematic error in caused by cluster shape assumes that H 0 each sample beta model cluster has a Ðxed shape ; deviations from constant shape within the clusters may introduce additional uncertainty or bias into this result.