We have deduced the cosmic microwave background (CMB) temperature in the Coma cluster (A1656, z=0.0231), and in A2163 (z=0.203) from spectral measurements of the Sunyaev-Zel'dovich (SZ) effect over four passbands at radio and microwave frequencies. The resulting temperatures at these redshifts are TComa=2.789−0.065+0.080 K and TA2163=3.377−0.102+0.101 K, respectively. These values confirm the expected relation T(z)=T0(1+z), where T0=2.725±0.002 K is the value measured by the COBE/FIRAS experiment. Alternative scaling relations that are conjectured in non-standard cosmologies can be constrained by the data; for example, if T(z)=T0(1+z)1−a or T(z)=T0[1+(1+d)z], then a=−0.16−0.32+0.34 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.
@article{arxiv.astro-ph/0208027,
title = {Cosmic Microwave Background Temperature at Galaxy Clusters},
author = {E. S. Battistelli and M. De Petris and L. Lamagna and F. Melchiorri and E. Palladino and G. Savini and A. Cooray and A. Melchiorri and Y. Rephaeli and M. Shimon},
journal= {arXiv preprint arXiv:astro-ph/0208027},
year = {2009}
}