IMPACT OF CHANDRA CALIBRATION UNCERTAINTIES ON GALAXY CLUSTER TEMPERATURES: APPLICATION TO THE HUBBLE CONSTANT

We perform a uniform, systematic X-ray spectroscopic analysis of a sample of 38 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 Chandra calibration on cluster spectral properties and the implications 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 H0. 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, H0 ∼ 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.