Three-year Wilkinson Microwave Anisotropy Probe (WMAP) observations:: Polarization analysis

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 nu less than or similar to P 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 approximate to 5 mu K at 22 GHz to less than or similar to 0.6 mu K at 61 GHz. By comparison, the levels of intrinsic CMB polarization for a Lambda CDM model with an optical depth of tau = 0.09 and assumed tensor-to-scalar ratio r = 0.3 are approximate to 0.3 mu K for E-mode polarization and approximate to 0.1 mu K 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)/2 pi = 0.086 +/- 0.29 ( mu K)(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 tau we find tau = 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 tau = 0.09 +/- 0.03. Marginalization over the foreground subtraction affects this value by delta(tau) < 0.01. We see no evidence for B modes, limiting them to l( l + 1)C-l=< 2-6 >(BB)/2 pi = -0.04 +/- 0.03 ( mu K)(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 Omega(GW)h(2) < 5 x 10(-12). From the full WMAP analysis, we find r < 0.55 ( 95% CL) corresponding to a limit of Omega(GW)h(2) < 1 x 10(-12) ( 95% CL). The limit on r is approaching the upper bound of predictions for some of the simplest models of inflation, r similar to 0.3.