Wehus, I. K. and Ackerman, L. and Eriksen, H. K. and Groeneboom, N. E. (2009) The Effect of Asymmetric Beams in the Wilkinson Microwave Anisotropy Probe Experiment. Astrophysical Journal, 707 (1). pp. 343-353. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20091215-151607394
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We generate simulations of the cosmic microwave background (CMB) temperature field as observed by the Wilkinson Microwave Anisotropy Probe (WMAP) satellite, taking into account the detailed shape of the asymmetric beams and scanning strategy of the experiment, and use these to re-estimate the WMAP beam transfer functions. This method avoids the need of artificially symmetrizing the beams, as done in the baseline WMAP approach, and instead measures the total convolution effect by direct simulation. We find only small differences with respect to the nominal transfer functions, typically less than 1% everywhere, and less than 0.5% at ℓ < 400. The net effect on the CMB power spectrum is less than 0.6%. The effect on all considered cosmological parameters is negligible. For instance, we find that the spectral index of scalar perturbations after taking into account the beam asymmetries is n_s = 0.964 ± 0.014, corresponding to a negative shift of –0.1σ compared to the previously released WMAP results. Our CMB sky simulations are made publicly available and can be used for general studies of asymmetric beam effects in the WMAP data.
|Additional Information:||© 2009 The American Astronomical Society. Received 2009 April 25; accepted 2009 October 21; published 2009 November 20. The authors thank Ned Wright for very useful and stimulating discussions, which eventually led to the conception of this project, and the referee for very useful comments. We also thank Kris G´orski, Sanjit Gupta, Gary Hinshaw, and Graca Rocha for interesting discussions, and the WMAP team for providing the required data for the project, including the beam pixel window function. L.A. thanks the Institute of Theoretical Astrophysics, Oslo, for its generous hospitality during her visit to Norway. I.K.W., H.K.E., and N.E.G. acknowledge financial support from the Research Council of Norway. The computations presented in this paper were carried out on Titan, a cluster owned and maintained by the University of Oslo and NOTUR. Some of the results in this paper have been derived using the HEALPix (G´orski et al. 2005) software and analysis package. We acknowledge use of the Legacy Archive for Microwave Background Data Analysis (LAMBDA). Support for LAMBDA is provided by the NASA Office of Space Science.|
|Subject Keywords:||cosmic microwave background; cosmology: observations; methods: statistical|
|Official Citation:||The Effect of Asymmetric Beams in the Wilkinson Microwave Anisotropy Probe Experiment I. K. Wehus, L. Ackerman, H. K. Eriksen, and N. E. Groeneboom 2009 ApJ 707 343-353 doi: 10.1088/0004-637X/707/1/343|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||04 Jan 2010 23:06|
|Last Modified:||26 Dec 2012 11:39|
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