Measurement of the electron-pressure profile of galaxy clusters in 3 year Wilkinson microwave anisotropy probe (WMAP) data

Using 3 year WMAP data at the locations of similar to 700 X-ray-selected clusters, we have detected the amplitude of the thermal Sunyaev-Zeldovich (TSZ) effect at the 15 sigma level, the highest statistical significance reported so far. Owing to the large size of our cluster sample, we are able to detect the corresponding cosmic microwave background distortions out to large cluster-centric radii. The region over which the TSZ signal is detected is, on average, 4 times larger in radius than the X-ray-emitting region, extending to similar to 3 h(70)(-1) Mpc. We show that an isothermal b- model does not fit the electron pressure at large radii; instead, the baryon profile is consistent with the Navarro-Frenk-White profile, which is expected for dark matter in the concordance Lambda CDM model. The Xray temperature at the virial radius of the clusters falls by a factor similar to 3-4 from the central value, depending on the cluster concentration parameter. Our results suggest that cluster dynamics at large radii is dominated by dark matter and is well described by Newtonian gravity.