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 cosmol ogical probe have been based on an approximate nonrelativistic treatme nt of the effect. An exact relativistic calculation, which is describe d in detail, is particularly important for the correct determinations of the Hubble constant and peculiar velocities of clusters. A number o f studies of CMB anisotropy induced by clusters have been carried out; by most accounts this is predicted to constitute an appreciable compo nent of the overall anisotropy on scales of a few arcminutes. Statisti cally significant detections of the effect in more than a dozen cluste rs are reviewed; in addition to the traditional single-dish radio meas urements, these now include interferometric observations with the Ryle and OVRO arrays and the high-frequency measurements with the SUZIE ex periment. The combination of these and X-ray measurements yield a mean (unweighted) value of 58 +/- 6 km s(-1) Mpc(-1) for the Hubble consta nt.