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Credit Physics Department at Durham University

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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.

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Has Jupiter sent cosmology down a false trail?

It's supposed to be the "gold standard" of evidence supporting the standard model of cosmology - including dark matter, dark energy and the exponential expansion after the big bang known as inflation.
But could it be wrong? Might misleading measurements by NASA's Wilkinson Microwave Anisotropy Probe (WMAP) have been leading us towards the wrong theory of cosmology? One astrophysicist thinks so, and he says the planet Jupiter is to blame though others insist that there is nothing amiss.
WMAP detects photons of the cosmic microwave background, the "echo" of the big bang, and these measurements are used to map the temperature of the sky. Ripples in the map are used to calculate a spectrum that produces a near-perfect fit to the standard model of cosmology.

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L

Posts: 131433
Date:
Permalink  
 

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)

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Found: Hawking's initials written into the universe
The latest version of the cosmic microwave background reveals some hidden surprises.

Is Stephen Hawking a galactic graffiti artist? Hidden away in the cosmic microwave background, the afterglow of the big bang, the initials "SH" are clear to view (see picture, right). We took a closer look and spotted a donkey, a deer and a parrot.
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SH2.jpg

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Cosmic microwave background
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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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Presented by Azriel Goldschmidt and Keith Beattie.
The South Pole, besides being an interesting place in its own right, is uniquely suited for Neutrino Astronomy and a challenging place to locate a cosmic ray detector and corresponding compute cluster. Azriel Goldschmit and Keith Beattie, respectively a particle physicist and computer systems engineer at Lawrence Berkeley National Labs, will present the physics motivation behind building a kilometre cube neutrino detector at the South Pole, go into some of the details of the data-acquisition system running there and describe travel to, work and life at the South Pole.

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Cosmic Microwave Background
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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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Mapping the Universe with Helium
Cosmologists talk about the cosmic microwave background radiation, their snapshot of the universe at the tender age of 400,000 years, so much that it might seem pretty well mined out by now. After all, the European Space Agency intends for its new Planck satellite to extract "essentially all the information available" in the radiation's spatial patterns. But cosmologists looking beyond Planck say the radiation has a barely explored aspect that, if it could be observed with enough precision, would reveal new details about the early universe: its spectrum.
Astronomers routinely use the rainbow of colours emitted by the sun and other stars to determine their composition. At the American Astronomical Society meeting this past January, renowned astrophysicist Rashid Sunyaev of the Max Planck Institute for Astrophysics in Garching, Germany, argued that a successor to Planck might pick up similar fingerprints in the background radiation, the spectrum of which currently seems completely featureless and generic.

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Cosmic background radiation
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Robert W. Wilson was the co-discoverer in 1964 of the 3K Cosmic Background Radiation which originated in the Big Bang and for which he shared the 1978 Nobel Prize in Physics.
Prior to the 20th century, cosmology was the study of objects in the Universe, not the physics of the Universe as a whole. In this talk Wilson reviewed the development of cosmology in the first half of the 20th century, discussed the discovery of the cosmic microwave background radiation at Bell Labs and several near misses, which preceded them.
This video presentation, part of the Opening Ceremony of the International Year of Astronomy 2009 held in UNESCO, Paris is featured on the IAF channel courtesy of the International Astronomical Union and UNESCO. The event was co-ordinated by the Observatoire de Paris.

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