Impact of Chandra calibration uncertainties on galaxy cluster temperatures: application to the Hubble Constant

TL;DR

This study assesses how uncertainties in Chandra X-ray telescope calibration affect galaxy cluster temperature measurements and the derived Hubble constant, highlighting calibration's critical role in precision cosmology.

Contribution

It systematically analyzes the impact of different Chandra calibrations on cluster temperatures and Hubble constant estimates, emphasizing calibration's influence on cosmological measurements.

Findings

Cluster temperatures vary by ~6-13% between calibrations.

Hubble constant estimates shift by +10% to -13% with calibration changes.

Newer calibrations suggest a lower Hubble constant around 60 km s-1 Mpc-1.

Abstract

We perform a uniform, systematic analysis of a sample of 38 X-ray galaxy clusters with three different Chandra calibrations. The temperatures change systematically between calibrations. Cluster temperatures change on average by roughly ~6% for the smallest changes and roughly ~13% for the more extreme changes between calibrations. We explore the effects of the changing cluster spectral properties on Sunyaev-Zel'dovich effect (SZE) and X-ray determinations of the Hubble constant. The Hubble parameter changes by +10% and -13% between the current calibration and two previous Chandra calibrations, indicating that changes in the cluster temperature basically explain the entire change in H_0. Although this work focuses on the difference in spectral properties and resultant Hubble parameters between the calibrations, it is intriguing to note that the newer calibrations favor a lower value of the Hubble constant, H_0 ~ 60 km s-1 Mpc-1, typical of results from SZE/X-ray distances. Both galaxy clusters themselves and the details of the instruments must be known precisely to enable reliable precision cosmology with clusters, which will be feasible with combined efforts from ongoing observations and planned missions and observatories covering a wide range of wavelengths.