* Astronomy

Title: Beam profile sensitivity of the WMAP CMB power spectrum
Authors: U. Sawangwit, T. Shanks (Durham University, UK)
(Version v2)

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 in radius. 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\approx200 which is the scale of the first acoustic peak. The difference between the beam convolved C_l and the final C_l is ~70% at the scale of the first peak, rising to \approx400% 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 temperature maps. The radio sources show a significantly (3-4\sigma) 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 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. We also argue against the possibility that Eddington bias is affecting our results. The reasons for the difference between the radio source and the Jupiter beam profiles are therefore still unclear. If the radio source profiles were then used to define the WMAP beam, there could be a significant 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.

Read more (77kb, PDF)

Title: Beam profile sensitivity of the WMAP CMB power spectrum
Authors: U. Sawangwit, T. Shanks (Durham University, UK)
(Version v2)

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 in radius. This means that even though the core width corresponds to wavenumber l\approx1800, the form of the beam still significantly affects the WMAP results even at l\approx200 which is the scale of the first acoustic peak. The difference between the beam convolved C_l and the final 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 temperature maps. The radio sources show a significantly (3-4\sigma) 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 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. We also argue against the possibility that Eddington bias is affecting our results. The reasons for the difference between the radio source and the Jupiter beam profiles are therefore still unclear. If the radio source profiles were then used to define the WMAP beam, there could be a significant 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.

Read more (77kb, PDF)

High-precision measurements confirm cosmologists standard view of universe
An international team that includes the University of Chicago has unveiled a detailed picture of the seeds of structures in the universe. These measurements of the cosmic microwave background (CMB) - a faintly glowing relic of the hot, dense, young universe - put limits on proposed alternatives to the standard model of cosmology and provide further support for that model, confirming that dark matter and dark energy make up 95 percent of everything in existence, while ordinary matter makes up just five percent.

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Planck telescope's first glimpses
The European telescope sent far from Earth to study the oldest light in the Universe has returned its first images.
The Planck observatory, launched in April, is surveying radiation that first swept out across space just 380,000 years after the Big Bang.

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