COBE, “Followed-up” by WMAP COBE WMAP COBE 1989 WMAP 2001 [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. Press Release from the Nobel Foundation
So, It ’ s Been Three Years Since The First Data Release in 2003. What Is New Now?
POLARIZATION DATA!! CMB is not only anisotropic, but also polarized.
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!!
The Angular Power Spectrum CMB temperature anisotropy is very close to Gaussian (Komatsu et al., 2003); thus, its spherical harmonic transform, a lm, is also Gaussian. Since a lm is Gaussian, the power spectrum: completely specifies statistical properties of CMB.
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-modeB-mode Seljak & Zaldarriaga (1997); Kamionkowski, Kosowsky, Stebbins (1997)
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 anisotropic no net polarization net polarization
Boltzmann Equation Temperature anisotropy, , 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.
Primordial Gravity Waves Gravity waves also create quadrupolar temperature anisotropy -> Polarization Most importantly, GW creates B mode.
Power Spectrum Scalar T Tensor T Scalar E Tensor E Tensor B
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. z=1100, ～ 1 z ～ 11, ～ 0.1 First-star formation z=0 IONIZED REIONIZED NEUTRAL e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e-
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
Temperature Damping, and Polarization Generation “ Reionization Bump ” 22 e-e-
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 C l Masking Is Not Enough: Foreground Must Be Cleaned Rough fit to BB FG in 60GHz
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)
BB consistent with zero after FG removal. 3-sigma detection of EE. The “Gold” multipoles: l=3,4,5,6.
Parameter Determination (ML): 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
Parameter Determination (Mean): First Year vs Three Years ML and Mean agree better for the 3yr data. –Degeneracy broken!
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.
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) Phase Shift Amplitude
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
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)
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 = 0.088 +- 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.
Degeneracy Finally Broken: Negative Tilt & Low Fluctuation Amplitude Degeneracy Line from Temperature Data Alone Polarization Data Nailed Tau Temperature Data Constrain “ 8 exp(- )” Lower Polarization Nailed Tau Lower 3rd peak
Constraints on GW Our ability to constrain the amplitude of gravity waves is still coming mostly from the temperature spectrum. –r<0.55 (95%) The B-mode spectrum adds very little. WMAP would have to integrate for at least 15 years to detect the B-mode spectrum from inflation.
What Should WMAP Say About Inflation Models? Hint for ns<1 Zero GW The 1-d marginalized constraint from WMAP alone is ns=0.96+-0.02. GW>0 The 2-d joint constraint still allows for ns=1.
What Should WMAP Say About Flatness? Flatness, or very low Hubble ’ s constant? If H=30km/s/Mpc, a closed universe with Omega=1.3 w/o cosmological constant still fits the WMAP data.
What Should WMAP Say About Dark Energy? Not much! The CMB data alone cannot constrain w very well. Combining the large-scale structure data or supernova data breaks degeneracy between w and matter density.
What Should WMAP Say About Neutrino Mass? 3.04)
Understanding of –Noise, –Systematics, –Foreground, and Analysis techniques have significantly improved from the first- year release. A simple LCDM model fits both the temperature and polarization data very well. To-do list for the next data release (now working on the 5-year data) Understand FG and noise better. We are still using only 1/2 of the polarization data. These improvements, combined with more years of data, would further reduce the error on tau. Full 3-yr would give delta(tau)~0.02 Full 6-yr would give delta(tau)~0.014 (hopefully) This will give us a better estimate of the tilt, and better constraints on inflation. Summary Tau=0.09+-0.03