Cosmic Microwave Background Temperature evolution by Sunyev Zel'dovich Effect observations

Spectral observations of the Sunyaev-Zel’dovich (SZ) effect are now available for a few clusters of galaxies. We have deduced the cosmic microwave background (CMB) temperature using data of the Coma cluster (A1656, z =0.0231) and of A2163 (z = 0.203) over four bands at radio and microwave frequencies. The estimated temperatures at these redshifts are TComa = 2.789+0.080+/-0.065 K and TA2163 = 3.377+0.101+/-0.102 K, respectively. These values confirm the expected scaling T(z) = T0(1+z), where T0 = 2.725+/-0.002 K is the value measured by the COBE/FIRAS experiment. At the same time alternative CMB temperature evolutions as foreseen in non-standard cosmologies can be constrained by the data; for example, if T(z) = T0(1+z)^a or T(z) = T0[1+(1+d)z], then a = 0.16+0:34-0:32 and d = 0.17+/-0.36 (at 95% confidence). We briefly discuss future prospects for more precise SZ measurements of T(z) at higher redshifts.