2009ApJ...705.1122L

We have determined the cosmic microwave background temperature, T(z), at redshifts in the range 0.023-0.546, from multi-frequency measurements of the Sunyaev-Zeldovich (S-Z) effect toward 13 clusters. We extract the parameter α in the redshift scaling T(z) = T₀(1 + z)^1–α, which contrasts the prediction of the standard model (α = 0) with that in non-adiabatic evolution conjectured in some alternative cosmological models. The statistical analysis is based on two main approaches: using ratios of the S-Z intensity change, ΔI, thus taking advantage of the weak dependence of the ratios on intracluster gas properties, and using directly the ΔI measurements. In the former method, dependence on the Thomson optical depth and gas temperature is only second order in these quantities. In the second method, we marginalize over these quantities which appear to first order in the intensity change. The marginalization itself is done in two ways–by direct integrations and by a Monte Carlo Markov chain approach. Employing these different methods we obtain two sets of results that are consistent with α = 0, in agreement with the prediction of the standard model.