The Astrophysical Journal Supplement Series · 2011 · 1.3K citations · 52 references
(Abridged) We present the angular power spectra derived from the 7-year maps\nand discuss the cosmological conclusions that can be inferred from WMAP data\nalone. The third acoustic peak in the TT spectrum is now well measured by WMAP.\nIn the context of a flat LambdaCDM model, this improvement allows us to place\ntighter constraints on the matter density from WMAP data alone, and on the\nepoch of matter-radiation equality, The temperature-polarization (TE) spectrum\nis detected in the 7-year data with a significance of 20 sigma, compared to 13\nsigma with the 5-year data. The low-l EE spectrum, a measure of the optical\ndepth due to reionization, is detected at 5.5 sigma significance when averaged\nover l = 2-7. The BB spectrum, an important probe of gravitational waves from\ninflation, remains consistent with zero. The upper limit on tensor modes from\npolarization data alone is a factor of 2 lower with the 7-year data than it was\nusing the 5-year data (Komatsu et al. 2010). We test the parameter recovery\nprocess for bias and find that the scalar spectral index, ns, is biased high,\nbut only by 0.09 sigma, while the remaining parameters are biased by < 0.15\nsigma. The improvement in the third peak measurement leads to tighter lower\nlimits from WMAP on the number of relativistic degrees of freedom (e.g.,\nneutrinos) in the early universe: Neff > 2.7 (95% CL). Also, using WMAP data\nalone, the primordial helium mass fraction is found to be YHe = 0.28+0.14-0.15,\nand with data from higher-resolution CMB experiments included, we now establish\nthe existence of pre-stellar helium at > 3 sigma (Komatsu et al. 2010).\n
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