THE ATACAMA COSMOLOGY TELESCOPE: COSMOLOGICAL PARAMETERS FROM THE 2008 POWER SPECTRUM

By J. Dunkley, R. Hložek, Jonathan Sievers, V. Acquaviva, P. Ade, P. Aguirre, M. Amiri, J. Appel, L. Barrientos, E. Battistelli and 57 more. 2010

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We present cosmological parameters derived from the angular power spectrum of the cosmic microwave background (CMB) radiation observed at 148 GHz and 218 GHz over 296 deg2 with the Atacama Cosmology Telescope (ACT) during its 2008 season. ACT measures fluctuations at scales 500 < ℓ < 10, 000. We fit a model for the lensed CMB, Sunyaev–Zel'dovich (SZ), and foreground contribution to the 148 GHz and 218 GHz power spectra, including thermal and kinetic SZ, Poisson power from radio and infrared point sources, and clustered power from infrared point sources. At ℓ = 3000, about half the power at 148 GHz comes from primary CMB after masking bright radio sources. The power from thermal and kinetic SZ is estimated to be , where . The IR Poisson power at 148 GHz is (Cℓ = 5.5 ± 0.5 nK2), and a clustered IR component is required with , assuming an analytic model for its power spectrum shape. At 218 GHz only about 15% of the power, approximately 27 μK2, is CMB anisotropy at ℓ = 3000. The remaining 85% is attributed to IR sources (approximately 50% Poisson and 35% clustered), with spectral index α = 3.69 ± 0.14 for flux scaling as S(ν)∝να. We estimate primary cosmological parameters from the less contaminated 148 GHz spectrum, marginalizing over SZ and source power. The ΛCDM cosmological model is a good fit to the data (χ2/dof = 29/46), and ΛCDM parameters estimated from ACT+Wilkinson Microwave Anisotropy Probe (WMAP) are consistent with the seven-year WMAP limits, with scale invariant ns = 1 excluded at 99.7% confidence level (CL) (3σ). A model with no CMB lensing is disfavored at 2.8σ. By measuring the third to seventh acoustic peaks, and probing the Silk damping regime, the ACT data improve limits on cosmological parameters that affect the small-scale CMB power. The ACT data combined with WMAP give a 6σ detection of primordial helium, with YP = 0.313 ± 0.044, and a 4σ detection of relativistic species, assumed to be neutrinos, with Neff = 5.3 ± 1.3 (4.6 ± 0.8 with BAO+H0 data). From the CMB alone the running of the spectral index is constrained to be dns/dln k = −0.034 ± 0.018, the limit on the tensor-to-scalar ratio is r < 0.25 (95% CL), and the possible contribution of Nambu cosmic strings to the power spectrum is constrained to string tension Gμ < 1.6 × 10−7 (95% CL).

Subfields: Astronomy and Astrophysics

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Citations in the corpus

A review of axion inflation in the era of Planck (2013, methodology): “[64] obtained the limits on ξ∗ resulting from the WMAP7 [65] and the ACT [67] data.”
COSMOLOGICAL CONSTRAINTS FROM SUNYAEV–ZEL'DOVICH-SELECTED CLUSTERS WITH X-RAY OBSERVATIONS IN THE FIRST 178 deg2 OF THE SOUTH POLE TELESCOPE SURVEY (2011, background): “Recent measurements have shown a ∼2σ preference for increased damping in the tail of the CMB power spectrum (Dunkley et al. 2011; Keisler et al. 2011).”
Modified Gravity and Cosmology (2011, methodology): “• Measurements of the CMB anisotropies from large to small scales [664, 407], combined with measurements of galaxy clustering from the Sloan Digital Sky Survey (SDSS) [969], greatly favour a model with ΩΛ = 0.”
CMB at 2 × 2 order: the dissipation of primordial acoustic waves and the observable part of the associated energy release (2012, methodology): “The effect of Silk damping today is observed by CMB anisotropy experiments (Larson et al. 2011; Reichardt et al. 2009; Keisler et al. 2011; Dunkley et al. 2011).”
A MEASUREMENT OF SECONDARY COSMIC MICROWAVE BACKGROUND ANISOTROPIES WITH TWO YEARS OF SOUTH POLE TELESCOPE OBSERVATIONS (2011, methodology): “As in S11, we calculate the principal components of the full covariance matrix of this measurement and find that three eigenvectors are adequate to represent >99% of the covariance.”
A MEASUREMENT OF THE COSMIC MICROWAVE BACKGROUND DAMPING TAIL FROM THE 2500-SQUARE-DEGREE SPT-SZ SURVEY (2012, background): “The ACT+WMAP7 constraint, 0.813 ± 0.028 (Dunkley et al. 2011), is consistent with that from SPT+WMAP7, though we note that the WMAP7 data are used in both.”
NEW CONSTRAINTS ON COSMIC REIONIZATION FROM THE 2012 HUBBLE ULTRA DEEP FIELD CAMPAIGN (2013, background): “Both the Atacama Cosmology Telescope and the South Pole Telescope have placed upper limits on this signal (Dunkley et al. 2011; Reichardt et al. 2012).”
The Atacama Cosmology Telescope: Sunyaev-Zel'dovich selected galaxy clusters at 148 GHz from three seasons of data (2013, background): “While the B12 normalization lies somewhat below the UPP prediction, we note that even lower normalizations (such as that found in the Nonthermal20 model) are favored by recent measurements of the SZ contribution to the CMB angular power spectrum (Dunkley et al. 2011; Reichardt et al. 2012).”