### Abstract

This paper focuses on cosmological constraints derived from analysis of WMAP data alone. A simple ACDM 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_{A} = 0.742 ± 0.030, n_{s} = 0.963^{+0.014}_{-01015},ζ= 0.087 ± 0.017, and σ_{8} = 0.796 ± 0.036, with h = 0.719^{+0.026}_{-0.027} Withfive years of polarization data, we have measured theoptical depth to reionization, ζ > 0, at 5σ significance. The redshift of an instantaneous reionization is constrained to be z_{reloz} = 11.0 = 1.4 with 68% confidence. The 2σ lower limit is z_{reion} > 8.2, and the 3σ limit is z_{reioz} > 6.7. This excludes a sudden reionization of the universe at z = 6 at more than 3 .5σ significance, suggesting that reionization was an extended process. Using two methods for polarized foreground cleaning we get consistent estimates for the optical depth, indicating an error due to the foreground treatment of ζ ~ 0.01. This cosmological model also fits small-scale cosmic microwave background (CMB) data, and a range of astronomical data measuring the expansion rate and clustering of matter in the universe. We find evidence for the first time in the CMB power spectrum for a nonzero cosmic neutrino background, or a background of relativistic species, with the standard three light neutrino species preferred over the best-fit ACDM model with N_{eff} = 0 at > 99.5% confidence, and N_{eff} 2.3 (95% confidence limit (CL)) when varied. The fiveyear WMAP data improve the upper limit on the tensor-to-scalar ratio, r < 0.43 (95% CL), for power-law models, and halve the limit on r for models with a running index, r < 0.58 (95% CL). With longer integration we find no evidence for a running spectral index, with dn_{s}/d ln k = -0.037 ± 0.028, and find improved limits on isocurvature fluctuations. The current WMAP-only limit on the sum of the neutrino masses is Σ m _{v}; 1.3 eV (95% CL), which is robust, to within 10%, to a varying tensor amplitude, running spectral index, or dark energy equation of state.

Original language | English (US) |
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Pages (from-to) | 306-329 |

Number of pages | 24 |

Journal | Astrophysical Journal, Supplement Series |

Volume | 180 |

Issue number | 2 |

DOIs | |

State | Published - Sep 8 2009 |

### All Science Journal Classification (ASJC) codes

- Astronomy and Astrophysics
- Space and Planetary Science

### Keywords

- Cosmic microwave background
- Cosmology: observations
- Early universe
- Polarization

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## Cite this

*Astrophysical Journal, Supplement Series*,

*180*(2), 306-329. https://doi.org/10.1088/0067-0049/180/2/306