### Abstract

The Wilkinson Microwave Anisotropy Probe (WMAP) has mapped the entire sky in five frequency bands between 23 and 94 GHz with polarization-sensitive radiometers. We present 3 year full-sky maps of the polarization and analyze them for foreground emission and cosmological implications. These observations open up a new window for understanding how the universe began and help set a foundation for future observations. WMAP observes significant levels of polarized foreground emission due to both Galactic synchrotron radiation and thermal dust emission. Synchrotron radiation is the dominant signal at l < 50 and ν ≲ 40 GHz, while thermal dust emission is evident at 94 GHz. The least contaminated channel is at 61 GHz. We present a model of polarized foreground emission that captures the large angular scale characteristics of the microwave sky. After applying a Galactic mask that cuts 25.7% of the sky, we show that the high Galactic latitude rms polarized foreground emission, averaged over l = 4-6, ranges from ≈ 5 μK at 22 GHz to ≲0.6 μK at 61 GHz. By comparison, the levels of intrinsic CMB polarization for a ACDM model with an optical depth of τ = 0.09 and assumed tensor-to-scalar ratio r = 0.3 are ≈0.3 μK for E-mode polarization and ≈0.1 μK for B-mode polarization. To analyze the maps for CMB polarization at l < 16, we subtract a model of the foreground emission that is based primarily on a scaling WMAP's 23 GHz map. In the foreground-corrected maps, we detect l(l + 1)C _{l=〈2-6〉}^{EE}/2π = 0.086 ± 0.029 (μK)^{2}. This is interpreted as the result of rescattering of the CMB by free electrons released during reionization at z_{r} = 10.9 _{-2.3}^{+2.7} for a model with instantaneous reionization. By computing the likelihood of just the EE data as a function of τ we find τ = 0.10 ± 0.03. When the same EE data are used in the full six-parameter fit to all WMAP data (TT, TE, EE), we find τ = 0.09 ± 0.03. Marginalization over the foreground subtraction affects this value by δτ < 0.01. We see no evidence for B modes, limiting them to l(l + 1)C_{l=〈2-6〉}^{BB}/2π = -0.04 ± 0.03 (μK)^{2}. We perform a template fit to the E-mode and B-mode data with an approximate model for the tensor scalar ratio. We find that the limit from the polarization signals alone is r < 2.2 (95% CL), where r is evaluated at k = 0.002 Mpc^{-1}. This corresponds to a limit on the cosmic density of gravitational waves of Ω_{GW}h^{2} < 5 × 10^{-12}. From the full WMAP analysis, we find r < 0.55 (95% CL) corresponding to a limit of Ω_{GW}h^{2} < 1 × 10^{-12} (95% CL). The limit on r is approaching the upper bound of predictions for some of the simplest models of inflation, r ∼ 0.3.

Original language | English (US) |
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Pages (from-to) | 335-376 |

Number of pages | 42 |

Journal | Astrophysical Journal, Supplement Series |

Volume | 170 |

Issue number | 2 |

DOIs | |

State | Published - Jun 1 2007 |

### All Science Journal Classification (ASJC) codes

- Astronomy and Astrophysics
- Space and Planetary Science

### Keywords

- Cosmic microwave background
- Cosmology: observations
- Polarization

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## Cite this

*Astrophysical Journal, Supplement Series*,

*170*(2), 335-376. https://doi.org/10.1086/513699