Measurement of the Sunyaev-Zel'dovich Effect toward Abell 2218 at 36 GHz

We performed a millimeter-wave observation of the Sunyaev-Zel'dovich effect toward a moderately distant cD cluster of galaxies, Abell 2218, at 36 GHz using the Nobeyama 45-m telescope. The antenna temperature decrement of the cosmic microwave background radiation (CMB) was measured to be ΔTA ^* = −0.52 ± 0.15 mK at the central peak position of X-ray emission in the cluster. Assuming that the hot gas in the cluster has isothermality, spherical symmetry, and the β-model density distribution, the Sunyaev-Zel'dovich effect is inferred to be ΔT0RJ = −0.68 ± 0.19 mK at the Rayleigh-Jeans limit. A combination of this Sunyaev-Zel'dovich effect and X-ray surface brightness suggests that the Hubble constant is H0 (q0 = 0.5) = 54⁺⁵¹−21 km s⁻¹ Mpc⁻¹.