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Polarized Light in the Cosmic Microwave Background: WMAP Three-year Results

Polarized Light in the Cosmic Microwave Background: WMAP Three-year Results. Eiichiro Komatsu (UT Austin) Colloquium at U. of Minnesota November 3, 2006. Full Sky Microwave Map. Penzias & Wilson, 1965. Uniform, “ Fossil ” Light from the Big Bang Isotropic Unpolarized.

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Polarized Light in the Cosmic Microwave Background: WMAP Three-year Results

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  1. Polarized Light in the Cosmic Microwave Background: WMAP Three-year Results Eiichiro Komatsu (UT Austin) Colloquium at U. of Minnesota November 3, 2006

  2. Full Sky Microwave Map Penzias & Wilson, 1965 • Uniform, “Fossil” Light from the Big Bang • Isotropic • Unpolarized Galactic Anti-center Galactic Center

  3. A. Penzias & R. Wilson, 1965

  4. Helium Superfluidity T = 2.17 K CMB T = 2.73 K

  5. COBE/FIRAS, 1990 Perfect blackbody = Thermal equilibrium = Big Bang

  6. COBE/DMR, 1992 Isotropic? Gravity is STRONGER in cold spots: DT/T~F

  7. COBE, “Followed-up” by WMAP COBE 1989 COBE Press Release from the Nobel Foundation [COBE’s] measurements also marked the inception of cosmology as a precise science. It was not long before it was followed up, for instance by the WMAP satellite, which yielded even clearer images of the background radiation. WMAP WMAP 2001

  8. David Wilkinson (1935~2002) • Science Team Meeting, July, 2002 • Plotted the “second point” (3.2cm) on the CMB spectrum • The first confirmation of a black-body spectrum (1966) • Made COBE and MAP happen and be successful • “Father of CMB Experiment” • MAP has become WMAP in 2003

  9. So, It’s Been Three Years Since The First Data Release in 2003. What Is New Now?

  10. POLARIZATION DATA!! Not only anisotropic, but also polarized.

  11. The Wilkinson Microwave Anisotropy Probe • A microwave satellite working at L2 • Five frequency bands • K (22GHz), Ka (33GHz), Q (41GHz), V (61GHz), W (94GHz) • Multi-frequency is crucial for cleaning the Galactic emission • The Key Feature: Differential Measurement • The technique inherited from COBE • 10 “Differencing Assemblies” (DAs) • K1, Ka1, Q1, Q2, V1, V2, W1, W2, W3, & W4, each consisting of two radiometers that are sensitive to orthogonal linear polarization modes. • Temperature anisotropy is measured by single difference. • Polarization anisotropy is measured by double difference. POLARIZATION DATA!!

  12. WMAP Three Year Papers

  13. K band (22GHz)

  14. Ka Band (33GHz)

  15. Q Band (41GHz)

  16. V Band (61GHz)

  17. W Band (94GHz)

  18. The Angular Power Spectrum • CMB temperature anisotropy is very close to Gaussian (Komatsu et al., 2003); thus, its spherical harmonic transform, alm, is also Gaussian. • Since alm is Gaussian, the power spectrum: completely specifies statistical properties of CMB.

  19. WMAP 3-yr Power Spectrum

  20. What Temperature Tells Us Distance to z~1100 Baryon-to-Photon Ratio Dark Energy/ New Physics? Matter-Radiation Equality Epoch

  21. CMB to Cosmology Low Multipoles (ISW) &Third Baryon/Photon Density Ratio

  22. K Band (23 GHz) Dominated by synchrotron; Note that polarization direction is perpendicular to the magnetic field lines.

  23. Ka Band (33 GHz) Synchrotron decreases as n-3.2 from K to Ka band.

  24. Q Band (41 GHz) We still see significant polarized synchrotron in Q.

  25. V Band (61 GHz) The polarized foreground emission is also smallest in V band. We can also see that noise is larger on the ecliptic plane.

  26. W Band (94 GHz) While synchrotron is the smallest in W, polarized dust (hard to see by eyes) may contaminate in W band more than in V band.

  27. Polarization Mask fsky=0.743

  28. Seljak & Zaldarriaga (1997); Kamionkowski, Kosowsky, Stebbins (1997) Jargon: E-mode and B-mode • Polarization has directions! • One can decompose it into a divergence-like “E-mode” and a vorticity-like “B-mode”. E-mode B-mode

  29. Polarized Light Un-filtered Polarized Light Filtered

  30. Physics of CMB Polarization • Thomson scattering generates polarization, if and only if… • Temperature quadrupole exists around an electron • Where does quadrupole come from? • Quadrupole is generated by shear viscosity of photon-baryon fluid. electron isotropic no net polarization anisotropic net polarization

  31. Boltzmann Equation • Temperature anisotropy, Q, can be generated by gravitational effect (noted as “SW” = Sachs-Wolfe, 1967) • Linear polarization (Q & U) is generated only by scattering (noted as “C” = Compton scattering). • Circular polarization (V) is not generated by Thomson scattering.

  32. Primordial Gravity Waves • Gravity waves also create quadrupolar temperature anisotropy -> Polarization • Most importantly, GW creates B mode.

  33. Power Spectrum Scalar T Tensor T Scalar E Tensor E Tensor B

  34. Polarization From Reionization • CMB was emitted at z~1100. • Some fraction of CMB was re-scattered in a reionized universe. • The reionization redshift of ~11 would correspond to 365 million years after the Big-Bang. e- e- e- e- e- e- IONIZED z=1100, t～1 e- e- e- e- e- NEUTRAL First-star formation z～11, t～0.1 REIONIZED e- e- e- e- z=0

  35. Measuring Optical Depth • Since polarization is generated by scattering, the amplitude is given by the number of scattering, or optical depth of Thomson scattering: which is related to the electron column number density as

  36. Polarization from Reioniazation “Reionization Bump” 2

  37. Masking Is Not Enough: Foreground Must Be Cleaned • Outside P06 • EE (solid) • BB (dashed) • Black lines • Theory EE • tau=0.09 • Theory BB • r=0.3 • Frequency = Geometric mean of two frequencies used to compute Cl Rough fit to BB FG in 60GHz

  38. Clean FG • Only two-parameter fit! • Dramatic improvement in chi-squared. • The cleaned Q and V maps have the reduced chi-squared of ~1.02 per DOF=4534 (outside P06)

  39. 3-sigma detection of EE. The “Gold” multipoles: l=3,4,5,6. BB consistent with zero after FG removal.

  40. Parameter Determination: First Year vs Three Years • The simplest LCDM model fits the data very well. • A power-law primordial power spectrum • Three relativistic neutrino species • Flat universe with cosmological constant • The maximum likelihood values very consistent • Matter density and sigma8 went down slightly

  41. Null Tests • It’s very powerful to have three years of data. • Year-year differences must be consistent with zero signal. • yr1-yr2, yr2-yr3, and yr3-yr1 • We could not do this null test for the first year data. • We are confident that we understand polarization noise to a couple of percent level. • Statistical isotropy • TB and EB must be consistent with zero. • Inflation prior… • We don’t expect 3-yr data to detect any BB.

  42. Data Combination (l<23) • We used Ka, Q, V, and W for the 1-yr TE analysis. • We use only Q and V for the 3-yr polarization analysis. • Despite the fact that all of the year-year differences at all frequencies have passed the null tests, the 3-yr combined power spectrum in W band shows some anomalies. • EE at l=7 is too high. We have not identified the source of this anomalous signal. (FG is unlikely.) • We have decided not to use W for the 3-yr analysis. • The residual synchrotron FG is still a worry in Ka. • We have decided not to use Ka for the 3-yr analysis. • KaQVW is ~1.5 times more sensitive to tau than QV. • Therefore, the error reduction in tau by going from the first-year (KaQVW) to three-year analysis (QV) is not as significant as one might think from naïve extrapolation of the first-year result. • There is also another reason why the three-year error is larger (and more accurate) – next slide.

  43. Correlated Noise • At low l, noise is not white. • 1/f noise increases noise at low l • See W4 in particular. • Scan pattern selectively amplifies the EE and BB spectra at particular multipoles. • The multipoles and amplitude of noise amplification depend on the beam separation, which is different from DA to DA. Red: white noise model (used in the first-year analysis) Black: correlated noise model (3-yr model)

  44. Low-l TE Data: Comparison between 1-yr and 3-yr • 1-yr TE and 3-yr TE have about the same error-bars. • 1yr used KaQVW and white noise model • Errors significantly underestimated. • Potentially incomplete FG subtraction. • 3yr used QV and correlated noise model • Only 2-sigma detection of low-l TE.

  45. High-l TE Data • The amplitude and phases of high-l TE data agree very well with the prediction from TT data and linear perturbation theory and adiabatic initial conditions. (Left Panel: Blue=1yr, Black=3yr) Amplitude Phase Shift

  46. High-l EE Data • When QVW are coadded, the high-l EE amplitude relative to the prediction from the best-fit cosmology is 0.95 +- 0.35. • Expect ~4-5sigma detection from 6-yr data. WMAP: QVW combined

  47. t1st year vs 3rd year • Tau is almost entirely determined by the EE from the 3-yr data. • TE adds very little. • Dotted: Kogut et al.’s stand-alone tau analysis from TE • Grey lines: 1-yr full analysis (Spergel et al. 2003)

  48. Tau is Constrained by EE • The stand-alone analysis of EE data gives • tau = 0.100 +- 0.029 • The stand-alone analysis of TE+EE gives • tau = 0.092 +- 0.029 • The full 6-parameter analysis gives • tau = 0.093 +- 0.029 (Spergel et al.; no SZ) • This indicates that the stand-alone EE analysis has exhausted most of the information on tau contained in the polarization data. • This is a very powerful statement: this immediately implies that the 3-yr polarization data essentially fixes tau independent of the other parameters, and thus can break massive degeneracies between tau and the other parameters.

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