View article

This paper focuses on cosmological constraints derived from analysis of WMAP data alone. A simple ΛCDM cosmological model fits the five-year WMAP temperature and polarization data. The basic parameters of the model are consistent with the three-year data and now better constrained: Ω b h 2= 0.02273±0.00062, Ω c h 2= 0.1099±0.0062, Ω Λ= 0.742±0.030, n s= 0.963+ 0.014− 0.015, τ= 0.087±0.017, and σ 8= 0.796±0.036, with h= 0.719+ 0.026− 0.027. With five years of polarization data, we have measured the optical depth to reionization, τ> 0, at 5σ significance. The redshift of an instantaneous reionization is constrained to be z reion= 11.0±1.4 with 68% confidence. The 2σ lower limit is z reion> 8.2, and the 3σ limit is z reion> 6.7. This excludes a sudden reionization of the universe at z= 6 at more than 3.5 σ significance, suggesting that reionization was an extended process. Using two methods for polarized …