Comptonization of the cosmic microwave background: The sunyaev-zeldovich effect

We review theoretical and observational work on Comptonization of the cosmic microwave background (CMB) radiation by hot gas in clusters of galaxies (the Sunyaev-Zeldovich effect). Uses of this important cosmological probe have been based on an approximate nonrelativistic treatment of the effect. An exact relativistic calculation, which is described in detail, is particularly important for the correct determinations of the Hubble constant and peculiar velocities of clusters. A number of studies of CMB anisotropy induced by clusters have been carried out; by most accounts this is predicted to constitute an appreciable component of the overall anisotropy on scales of a few arcminutes. Statistically significant detections of the effect in more than a dozen clusters are reviewed; in addition to the traditional single-dish radio measurements, these now include interferometric observations with the Ryle and OVRO arrays and the high-frequency measurements with the SUZIE experiment. The combination of these and X-ray measurements yield a mean (unweighted) value of 58 ± 6 km s^-1 Mpc^-1 for the Hubble constant.