Bayesian Component Separation and Cosmic Microwave Background Estimation for the Five-Year WMAP Temperature Data

Creators: Dickinson, C.; Eriksen, H. K.; Banday, A. J.; Jewell, J. B.; Górski, K. M.; Huey, G.; Lawrence, C. R.; O'Dwyer, I. J.; Wandelt, B. D.

Abstract

A well-tested and validated Gibbs sampling code, that performs component separation and cosmic microwave background (CMB) power spectrum estimation, was applied to the WMAP five-year data. Using a simple model consisting of CMB, noise, monopoles, and dipoles, a "per pixel" low-frequency power-law (fitting for both amplitude and spectral index), and a thermal dust template with a fixed spectral index, we found that the low-ℓ (ℓ < 50) CMB power spectrum is in good agreement with the published WMAP5 results. Residual monopoles and dipoles were found to be small (≾3 μK) or negligible in the five-year data. We comprehensively tested the assumptions that were made about the foregrounds (e.g., dust spectral index, power-law spectral index prior, templates), and found that the CMB power spectrum was insensitive to these choices. We confirm the asymmetry of power between the north and south ecliptic hemispheres, which appears to be robust against foreground modeling. The map of low-frequency spectral indices indicates a steeper spectrum on average (β = –2.97 ± 0.21) relative to those found at low (~GHz) frequencies.

Additional Information

© 2009 The American Astronomical Society. Received 2009 March 24; accepted 2009 August 13; published 2009 October 26. We acknowledge the use of the HEALPix software (Gorski 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). This work was partially performed at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. We acknowledge the use of the NOTUR super-computing facilities, the IPAC Planck cluster, and the Titan cluster owned and maintained by the University of Oslo. C.D. acknowledges support from the U.S. Planck project, which is funded by the NASA Science Mission Directorate. The work of C.D. was also supported in part by a STFC Advanced Fellowship. H.K.E. acknowledges financial support from the Research Council of Norway. B.D.W. was partially supported by NSF-AST 0507676 and NASA JPL 1236748.

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