ThreeYear Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Polarization Analysis
Abstract
The Wilkinson Microwave Anisotropy Probe (WMAP) has mapped the entire sky in five frequency bands between 23 and 94 GHz with polarizationsensitive radiometers. We present 3 year fullsky 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=46, ranges from ~5 μK at 22 GHz to <~0.6 μK at 61 GHz. By comparison, the levels of intrinsic CMB polarization for a ΛCDM model with an optical depth of τ=0.09 and assumed tensortoscalar ratio r=0.3 are ~0.3 μK for Emode polarization and ~0.1 μK for Bmode 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 foregroundcorrected maps, we detect l(l+1)C^{EE}_{l=<26>}/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^{+2.7}_{2.3} 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 sixparameter 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^{BB}_{l=<26>}/2π=0.04+/0.03 (μK)^{2}. We perform a template fit to the Emode and Bmode 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.
 Publication:

The Astrophysical Journal Supplement Series
 Pub Date:
 June 2007
 DOI:
 10.1086/513699
 arXiv:
 arXiv:astroph/0603450
 Bibcode:
 2007ApJS..170..335P
 Keywords:

 Cosmology: Cosmic Microwave Background;
 Cosmology: Observations;
 Polarization;
 Astrophysics
 EPrint:
 105 pgs, 28 figs. Accepted version of the 3year paper as posted to http://lambda.gsfc.nasa.gov/product/map/dr2/map_bibliography.cfm in January 2007