Ruling the Universe: an Improved Method for Measuring H0 with Galaxy Clusters

We present a new method of calculating the value of the Hubble constant (H0) from combined X-ray/SZE observations of clusters of galaxies. Values of H0 reported from cluster observations are systematically low compared to other methods. We show using a large sample of numerically simulated clusters at a variety of redshifts that the typically used method of calculating H0, which assumes the cluster gas to be isothermal, results in a 20-30% underestimate of the value of H0. The new method, which assumes the cluster gas temperature has a radial dependence described by a universal temperature profile, results in a value much closer to the true value of H0, the mean is a 38% overestimate. The new method also has greatly reduced scatter about the mean for all the clusters in the simulated catalog compared to the isothermal method. Additionally, we show that a variation on this technique shows promise in reliably determining the 3-D radial temperature profile of the cluster gas. Our new method requires no additional observational effort compared to the traditional technique. This simple change in the analysis of the cluster data results in values of H0 which are consistent with other observations. Subject headings: galaxies:clusters:general–cosmology:observations–hydrodynamics– methods:numerical–cosmology:cosmic microwave background