A Caltech Library Service

A Reanalysis of the 3 Year Wilkinson Microwave Anisotropy Probe Temperature Power Spectrum and Likelihood

Eriksen, H. K. and Huey, Greg and Saha, R. and Hansen, F. K. and Dick, J. and Banday, A. J. and Górski, K. M. and Jain, P. and Jewell, J. B. and Knox, L. and Larson, D. L. and O'Dwyer, I. J. and Souradeep, T. and Wandelt, B. D. (2007) A Reanalysis of the 3 Year Wilkinson Microwave Anisotropy Probe Temperature Power Spectrum and Likelihood. Astrophysical Journal, 656 (2). pp. 641-652. ISSN 0004-637X.

PDF - Published Version
See Usage Policy.


Use this Persistent URL to link to this item:


We analyze the 3 yr Wilkinson Microwave Anisotropy Probe (WMAP) temperature anisotropy data seeking to confirm the power spectrum and likelihoods published by the WMAP team. We apply five independent implementations of four algorithms to the power spectrum estimation and two implementations to the parameter estimation. Our single most important result is that we broadly confirm the WMAP power spectrum and analysis. Still, we do find two small but potentially important discrepancies. On large angular scales there is a small power excess in the WMAP spectrum (5%-10% at ell lesssim 30) primarily due to likelihood approximation issues between 13 ≤ ell lesssim 30. On small angular scales there is a systematic difference between the V- and W-band spectra (few percent at ell gtrsim 300). Recently, the latter discrepancy was explained by Huffenberger et al. (2006) in terms of oversubtraction of unresolved point sources. As far as the low-ell bias is concerned, most parameters are affected by a few tenths of a σ. The most important effect is seen in ns. For the combination of WMAP, ACBAR, and BOOMERANG, the significance of ns ≠ 1 drops from ~2.7 σ to ~2.3 σ when correcting for this bias. We propose a few simple improvements to the low-ell WMAP likelihood code, and introduce two important extensions to the Gibbs sampling method that allows for proper sampling of the low signal-to-noise ratio regime. Finally, we make the products from the Gibbs sampling analysis publicly available, thereby providing a fast and simple route to the exact likelihood without the need of expensive matrix inversions.

Item Type:Article
Related URLs:
URLURL TypeDescription
Additional Information:© 2007. The American Astronomical Society. Received 2006 June 5; accepted 2006 October 5. Print publication: Issue 2 (2007 February 20). We thank Eiichiro Komatsu and Gary Hinshaw for useful discussions and comments, and for their thorough work on reproducing the results presented here. We acknowledge use of the HEALPix software (Górski et al. 2005) and analysis package for deriving the results in this paper. We acknowledge use of the Legacy Archive for Microwave Background Data Analysis (LAMBDA). This work was partially performed at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. H.K.E. acknowledges financial support from the Research Council of Norway. B.D.W. acknowledges support through NSF grant AST-0507676 and NASA JPL subcontract 1236748. R.S., P.J., and T.S. acknowledge the use the IUCAA HPC facility for computations. T.S. thanks JPL for supporting the visit that helped initiate the collaboration.
Funding AgencyGrant Number
Research Council of NorwayUNSPECIFIED
National Science FoundationUNSPECIFIED
Subject Keywords:cosmic microwave background; cosmology: observations; methods: numerical
Issue or Number:2
Record Number:CaltechAUTHORS:ERIapj07a
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13009
Deposited By: Archive Administrator
Deposited On:15 Jan 2009 06:06
Last Modified:03 Oct 2019 00:33

Repository Staff Only: item control page