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Bayesian Analysis of an Anisotropic Universe Model: Systematics and Polarization

Groeneboom, Nicolaas E. and Ackerman, Lotty and Wehus, Ingunn Kathrine and Eriksen, Hans Kristian (2010) Bayesian Analysis of an Anisotropic Universe Model: Systematics and Polarization. Astrophysical Journal, 722 (1). pp. 452-459. ISSN 0004-637X.

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We revisit the anisotropic universe model previously developed by Ackerman, Carroll, and Wise (ACW), and generalize both the theoretical and computational framework to include polarization and various forms of systematic effects. We apply our new tools to simulated Wilkinson Microwave Anisotropy Probe (WMAP) data in order to understand the potential impact of asymmetric beams, noise misestimation, and potential zodiacal light emission. We find that neither has any significant impact on the results. We next show that the previously reported ACW signal is also present in the one-year WMAP temperature sky map presented by Liu & Li, where data cuts are more aggressive. Finally, we re-analyze the five-year WMAP data taking into account a previously neglected (−i)^(l−l')-term in the signal covariance matrix. We still find a strong detection of a preferred direction in the temperature map. Including multipoles up to ℓ = 400, the anisotropy amplitude for the W band is found to be g = 0.29 ± 0.031, nonzero at 9σ. However, the corresponding preferred direction is also shifted very close to the ecliptic poles at (l, b) = (96, 30), in agreement with the analysis of Hanson & Lewis, indicating that the signal is aligned along the plane of the solar system. This strongly suggests that the signal is not of cosmological origin, but most likely is a product of an unknown systematic effect. Determining the nature of the systematic effect is of vital importance, as it might affect other cosmological conclusions from the WMAP experiment. Finally, we provide a forecast for the Planck experiment including polarization.

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Additional Information:© 2010 American Astronomical Society. Received 2009 November 6; accepted 2010 August 13; published 2010 September 21. We thank Liu Hao and Ti-Pei Li for supplying us with their one-year WMAP data. We acknowledge use of the HEALPix7 software (Górski et al. 2005) and analysis package for deriving the results in this paper. We acknowledge the use of the Legacy Archive for Microwave Background Data Analysis (LAMBDA). Support for LAMBDA is provided by the NASA Office of Space Science. The authors acknowledge financial support from the Research Council of Norway.
Funding AgencyGrant Number
Research Council of NorwayUNSPECIFIED
NASA Office of Space ScienceUNSPECIFIED
Subject Keywords:cosmic background radiation; cosmology: observations; methods: numerical
Issue or Number:1
Classification Code:PACS: 98.80.Bp; 98.80.Cq; 98.70.Vc; 95.30.Gv
Record Number:CaltechAUTHORS:20101104-090601006
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Official Citation:Nicolaas E. Groeneboom et al 2010 ApJ 722 452 doi: 10.1088/0004-637X/722/1/452
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:20661
Deposited By: Ruth Sustaita
Deposited On:04 Nov 2010 16:34
Last Modified:03 Oct 2019 02:13

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