A Measurement of Gas Temperatures in Galaxy Clusters using the Relativistic Sunyaev-Zeldovich Effect

The hot gas in clusters of galaxies creates a distinctive spectral distortion in the cosmic microwave background (CMB) via the Sunyaev-Zeldovich (SZ) effect. To first order, the shape of the spectral distortion is fixed, but relativistic corrections (rSZ) introduce a dependence on the gas temperature. In this paper, we extract fluxes from a sample of 47 clusters in the Planck maps and make a ~5$\sigma$ detection of the rSZ effect by measuring the scaling relation between the SZ amplitude (a proxy for cluster mass) and the cluster temperature. Our measurement requires no prior knowledge of the clusters' gas temperatures and hence is an example of how the rSZ can be used to probe fundamental astrophysics. We find excellent agreement between our measurement and temperatures obtained with X-ray measurements.