THE ATACAMA COSMOLOGY TELESCOPE: COSMOLOGICAL PARAMETERS FROM THE 2008 POWER SPECTRUM
- Sub-Department of Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH (United Kingdom)
- Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, ON M5S 3H8 (Canada)
- Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08544 (United States)
- School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA (United Kingdom)
- Departamento de Astronomia y Astrofisica, Facultad de Fisica, PontificIa Universidad Catolica, Casilla 306, Santiago 22 (Chile)
- Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z4 (Canada)
- Joseph Henry Laboratories of Physics, Jadwin Hall, Princeton University, Princeton, NJ 08544 (United States)
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260 (United States)
- Code 553/665, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104 (United States)
- NIST Quantum Devices Group, Boulder, CO 80305 (United States)
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 deg{sup 2} 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 B{sub 3000} = 6.8 {+-} 2.9 {mu}K{sup 2}, where B{sub l}{identical_to}l(l + 1)C{sub l}/2{pi}. The IR Poisson power at 148 GHz is B{sub 3000} = 7.8 {+-} 0.7 {mu}K{sup 2} (C{sub l} = 5.5 {+-} 0.5 nK{sup 2}), and a clustered IR component is required with B{sub 3000} = 4.6 {+-} 0.9 {mu}K{sup 2}, assuming an analytic model for its power spectrum shape. At 218 GHz only about 15% of the power, approximately 27 {mu}K{sup 2}, is CMB anisotropy at l = 3000. The remaining 85% is attributed to IR sources (approximately 50% Poisson and 35% clustered), with spectral index {alpha} = 3.69 {+-} 0.14 for flux scaling as S({nu}){proportional_to}{nu}{sup {alpha}}. We estimate primary cosmological parameters from the less contaminated 148 GHz spectrum, marginalizing over SZ and source power. The {Lambda}CDM cosmological model is a good fit to the data ({chi}{sup 2}/dof = 29/46), and {Lambda}CDM parameters estimated from ACT+Wilkinson Microwave Anisotropy Probe (WMAP) are consistent with the seven-year WMAP limits, with scale invariant n{sub s} = 1 excluded at 99.7% confidence level (CL) (3{sigma}). A model with no CMB lensing is disfavored at 2.8{sigma}. 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 6{sigma} detection of primordial helium, with Y{sub P} = 0.313 {+-} 0.044, and a 4{sigma} detection of relativistic species, assumed to be neutrinos, with N{sub eff} = 5.3 {+-} 1.3 (4.6 {+-} 0.8 with BAO+H{sub 0} data). From the CMB alone the running of the spectral index is constrained to be dn{sub s} /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 G{mu} < 1.6 x 10{sup -7} (95% CL).
- OSTI ID:
- 21587513
- Journal Information:
- Astrophysical Journal, Vol. 739, Issue 1; Other Information: DOI: 10.1088/0004-637X/739/1/52; Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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