The intergalactic medium temperature and Compton y parameter

Abstract

(Abridged) The precision modeling of the thermal Sunyaev Zeldovich (SZ) effect and future high accuracy measurements will provide a powerful way to constrain the thermal history of the universe. In this paper, we combine high resolution adiabatic hydro simulations and analytical models to provide a precision modeling of the gas density weighted temperature ${\bar{T}}_g$ and the mean SZ Compton $y$ parameter. Simulation artifacts are quantified and corrected and our analytical model passes tests of various simulations and is able to predict ${\bar{T}}_g$ and $\bar{y}$ to several percent accuracy. For low matter density $\hat{I}›$CDM cosmology, the present ${\bar{T}}_g$ is $0.32(\ddot{I}{ƒ}_8/0.84{)}^{3.05-0.15\hat{I}{\text{c◯}}_m}(\hat{I}{\text{c◯}}_m/0.268{)}^{1.28-0.2\ddot{I}{ƒ}_8}\mathrm{keV}$. The mean $y$ parameter is $2.6\times 10^{-6}(\ddot{I}{ƒ}_8/0.84{)}^{4.1-2\hat{I}{\text{c◯}}_m}(\hat{I}{\text{c◯}}_m/0.268{)}^{1.28-0.2\ddot{I}{ƒ}_8}$. The current upper limit of $y<1.5\times 10^{-5}$ measured by FIRAS has already ruled out combinations of high $σ_8\ga 1.1$ and high $Ω_m\ga 0.5$.

11 pages, 12 figures, MNRAS, in press. Added more discussions about the halo model prediction