Observations of Sunyaev-Zel´dovich effect with Nobeyama 45-m telescope

We have three focal plane array receiver systems in the Nobeyama Radio Observatory 45-m radio telescope. These are S40M at 40 GHz, BEARS at 100 GHz, and NOBA at 150 GHz. A focal plane array receiver system at MM wavelengths is superior to a single receiver system in sensitivity and in the power of reducing atmospheric effects. The telescope and the array receivers cover the wide frequency range of the Rayleigh-Jeans region of the Sunyaev-Zel´dovich (S-Z) effect. The 45-m telescope is a most powerful tool for the observation of the S-Z effect. We have performed the ON-OFF observation of the S-Z effect toward eight X-ray bright galaxy clusters from z = 0.18 to 0.55 at 43 GHz as a pilot survey. The S-Z effects were detected for all clusters as a temperature decrement of 0.5-1 mK at the center. The Hubble constant is estimated to be H₀ = 64±17 km/s/Mpc for a flat ΛCDM cosmology, which shows good agreement with the values by other S-Z effect observations. The mapping observations of the S-Z effect are on-going. Although most of the observed images are roughly described by the isothermal spherical P-model density distribution, the deviation from the model seems to be large for clusters with an irregularity in the X-ray image rather than those without it.