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[0912.0524] Beam profile sensitivity of the WMAP CMB power spectrum
Authors:U. Sawangwit, T. Shanks (University of Durham, UK)
Abstract:Using the published WMAP 5-year data, we first show how sensitive the WMAP power spectra are to the form of the WMAP beam. It is well known that the beam profile derived from observations of Jupiter is non-Gaussian and indeed extends, in the W band for example, well beyond its 12.'6 FWHM core out to more than 1 degree. This means that even though the core width corresponds to wavenumber l=1800, the form of the beam still significantly affects the WMAP results even at l=200 which is the scale of the first acoustic peak. The difference between the raw C_l and the de-beamed C_l is ~70% at the scale of the first peak rising to ~400% at the scale of the second. New estimates of the Q, V and W-band beam profiles are then presented, based on a stacking analysis of the WMAP5 radio source catalogue and the temperature map. The radio sources show a significantly broader beam profile on scales of 10'-30' than that found by the WMAP team whose beam analysis is based on measurements of Jupiter. Beyond these scales the beam profiles from the radio sources are too noisy to give useful information. Furthermore, we find evidence that fainter radio sources imply wider beam profiles than the brighter sources and also tentative evidence for a non-linear relation between WMAP and ATCA/IRAM 95 GHz source fluxes. We discuss whether the wide beam profiles could be caused either by radio source extension or clustering and find that neither explanation is likely. The reasons for the difference between the radio source and the Jupiter beam profiles are still unclear. If the radio source profiles were then used to define the WMAP beam, there could be a dramatic change in the amplitude and position of even the first acoustic peak. It is therefore important to identify the reasons for the differences between these two beam profile estimates.
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Richard Lieu

Joined: 27 Nov 2005
Posts: 11
Affiliation: University of Alabama, Huntsville

PostPosted: December 06 2009  Reply with quote

This paper suggests that the WMAP beam may be wider than expected and that the systematic errors
on the CMB power spectrum may allow a much wider range of cosmological
models to be fitted than just LCDM.

The wider beam could also explain the lack of the expected SZ signal in
the WMAP W band, and could even be responsible (albeit in a subtle way) for the high degree of non-acoustic and non-foreground anisotropy on the 1-deg scale as reported in an ApJ paper of this month, 0904.2513.
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