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The Scalar Perturbation Spectral Index ns: WMAP Sensitivity to Unresolved Point Sources

Huffenberger, K. M. and Eriksen, H. K. and Hansen, H. K. and Banday, A. J. and Górski, K. M. (2008) The Scalar Perturbation Spectral Index ns: WMAP Sensitivity to Unresolved Point Sources. Astrophysical Journal, 688 (1). pp. 1-11. ISSN 0004-637X.

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Precision measurement of the scalar perturbation spectral index, ns, from the Wilkinson Microwave Anisotropy Probe (WMAP) temperature angular power spectrum requires the subtraction of unresolved point-source power. Here we reconsider this issue, attempting to resolve inconsistencies found in the literature. First, we note a peculiarity in the WMAP temperature likelihood’s response to the source correction: cosmological parameters do not respond to increased source errors. An alternative and more direct method for treating this error term acts more sensibly, and also shifts ns by ~0.3 σ closer to unity. Second, we re-examine the source fit used to correct the power spectrum. This fit depends strongly on the Galactic cut and the weighting of the map, indicating that either the source population or masking procedure is not isotropic. Jackknife tests appear inconsistent, causing us to assign large uncertainties to account for possible systematics. Third, we note that the WMAP team’s spectrum was computed with two different weighting schemes: uniform weights transition to inverse noise variance weights at l = 500. The fit depends on such weighting schemes, so different corrections apply to each multipole range. For the Kp2 mask used in cosmological analysis, we prefer source corrections A = 0.012 ± 0.005 µK^2 for uniform weighting and A = 0.015 ± 0.005 µK^2 for Nobs weighting. Correcting WMAP’s spectrum correspondingly, we compute cosmological parameters with our alternative likelihood, finding ns = 0.970 ± 0.017 and σ8 = 0.778 ± 0.045. This ns is only 1.8 σ from unity, compared to the ~2.6 σ WMAP 3 year result. Finally, an anomalous feature in the source spectrum at nl < 200 remains in the 3 year data, most strongly associated with the W band. We note the implications of these results for the 5 year data.

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Additional Information:© 2008. The American Astronomical Society. Received 2007 October 10; accepted 2008 June 25. We thank the WMAP team for useful discussions and for providing additional data. In particular we thank Gary Hinshaw, Michael Nolta, and Lyman Page, who suggested examining the effect of beam uncertainties. We acknowledge the helpful suggestion of an anonymous referee to consider the effect of multiple source populations. HEALPix software (Górski et al. 2005) was used to deriving some results in this paper. We also acknowledge use of the Legacy Archive for Microwave Background Data Analysis (LAMBDA). H.K.E. acknowledges financial support from the Research Council of Norway. This work was partially performed at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.
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Research Council of NorwayUNSPECIFIED
Subject Keywords:cosmic microwave background—cosmological parameters—cosmology: observations—methods: data analysis
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Record Number:CaltechAUTHORS:HUFapj08
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ID Code:12773
Deposited By: Archive Administrator
Deposited On:23 Dec 2008 00:50
Last Modified:03 Oct 2019 00:31

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