An improved approach to measuring H0 using X-ray and SZ observations of galaxy clusters

We present an improved method for predicting the Sunyaev-Zeldovich (SZ) effect in galaxy clusters from spatially resolved, spectroscopic X-ray data. Using the deprojected electron density and temperature profiles measured within a fraction of the virial radius, and assuming a Navarro-Frenk-White mass model, we show how the pressure profile of the X-ray gas can be extrapolated to large radii, allowing the Comptonization parameter profile for the cluster to be predicted precisely. We apply our method to Chandra observations of three X-ray-luminous, dynamically relaxed clusters with published SZ data: RX J1347.5-1145, Abell 1835 and Abell 478. Combining the predicted and observed SZ signals, we determine improved estimates for the Hubble constant from each cluster and obtain a weighted mean of H₀= 69 +/- 8kms^-1 Mpc^-1 for a cosmology with Ω_m= 0.3 and Ω_Λ= 0.7. This result is in good agreement with independent findings from the Hubble Key Project and the combination of cosmic microwave background and galaxy cluster data.