A Measurement of the Damping Tail of the Cosmic Microwave Background Power Spectrum with the South Pole Telescope

The Astrophysical Journal (Impact Factor: 5.99). 05/2011; 743(1). DOI: 10.1088/0004-637X/743/1/28
Source: arXiv
We present a measurement of the angular power spectrum of the cosmic microwave background (CMB) using data from the South Pole Telescope (SPT). The data consist of 790 deg2 of sky observed at 150 GHz during 2008 and 2009. Here we present the power spectrum over the multipole range 650 < ℓ < 3000, where it is dominated by primary CMB anisotropy. We combine this power spectrum with the power spectra from the seven-year Wilkinson Microwave Anisotropy Probe (WMAP) data release to constrain cosmological models. We find that the SPT and WMAP data are consistent with each other and, when combined, are well fit by a spatially flat, ΛCDM cosmological model. The SPT+WMAP constraint on the spectral index of scalar fluctuations is ns = 0.9663 ± 0.0112. We detect, at ~5σ significance, the effect of gravitational lensing on the CMB power spectrum, and find its amplitude to be consistent with the ΛCDM cosmological model. We explore a number of extensions beyond the ΛCDM model. Each extension is tested independently, although there are degeneracies between some of the extension parameters. We constrain the tensor-to-scalar ratio to be r < 0.21 (95% CL) and constrain the running of the scalar spectral index to be dns/dln k = –0.024 ± 0.013. We strongly detect the effects of primordial helium and neutrinos on the CMB; a model without helium is rejected at 7.7σ, while a model without neutrinos is rejected at 7.5σ. The primordial helium abundance is measured to be Yp = 0.296 ± 0.030, and the effective number of relativistic species is measured to be N
eff = 3.85 ± 0.62. The constraints on these models are strengthened when the CMB data are combined with measurements of the Hubble constant and the baryon acoustic oscillation feature. Notable improvements include ns = 0.9668 ± 0.0093, r < 0.17 (95% CL), and N
eff = 3.86 ± 0.42. The SPT+WMAP data show a mild preference for low power in the CMB damping tail, and while this preference may be accommodated by models that have a negative spectral running, a high primordial helium abundance, or a high effective number of relativistic species, such models are disfavored by the abundance of low-redshift galaxy clusters.
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    • "We use the BBN PArthENoPE code [96] [97] to compute the helium abundance, Y P , for different values of Ω b h 2 , ∆N ef f , ξ ν and changes of neutron and proton interaction rates due to We adapt the latest version of the publicly available package CosmoMC [81] for our cosmological analysis and use the following datasets and likelihood codes: • The Planck CMB anisotropy angular power spectrum, combined with WMAP-9 year polarization power spectrum at low ℓ [82] and the corresponding codes [1] [83]: Commander, that computes the low-l Planck likelihood, CamSpec, that computes the Planck likelihood for 50 ≤ l ≤ 2500, LowLike, that computes the likelihoods for 2 ≤ l ≤ 32 polarization data and Lensing, that computes the likelihoods from Planck lensing power spectrum for 40 ≤ l ≤ 400 [84]. • The high-l CMB data from Atacama Cosmology Telescope(ACT) [85] [86] and the South Pole Telescope (SPT) [87] [88]. "
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    • "Correlations were taken of the signals from pairs of horns, thus measuring the sky signal interferometrically. The 6 m diameter Atacama Cosmology Telescope (ACT) situated in the Atacama desert in Chile [109, 58] and the 10 m SPT (South Pole Telescope) located at the Amundsen-Scott South Pole Station in Antarctica [102, 199, 194] probe the microwave sky on very small angular scales, beyond the angular resolution of Planck. CMB observations are almost always diffraction limited, so that the angular resolution is inversely proportional to the telescope diameter. "
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    • "[71] [72] [73]. The latest CMB results of WMAP, SPT [74] and ACT [75] combined with BAO and HST gave N eff = 3.84 ± 0.40 at 68% C.L. [76]. Thus, although somehow controversial [77], rather than a constraint there seemed to be a 2-σ preference for a non-negligible amount of unaccounted dark radiation [78]. "
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