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Published June 2006 | Published
Journal Article Open

Non-Gaussianity in the Very Small Array cosmic microwave background maps with smooth goodness-of-fit tests

Abstract

We have used the Rayner and Best smooth tests of goodness-of-fit to study the Gaussianity of the Very Small Array (VSA) data. These tests are designed to be sensitive to the presence of 'smooth' deviations from a given distribution, and are applied to the data transformed into normalized signal-to-noise eigenmodes. In a previous work, they have been already adapted and applied to simulated observations of interferometric experiments. In this paper, we extend the practical implementation of the method to deal with mosaiced observations, by introducing the Arnoldi algorithm. This method permits us to solve large eigenvalue problems with low computational cost. Out of the 41 published VSA individual pointings dedicated to cosmological [cosmic microwave background (CMB)] observations, 37 are found to be consistent with Gaussianity, whereas four pointings show deviations from Gaussianity. In two of them, these deviations can be explained as residual systematic effects of a few visibility points which, when corrected, have a negligible impact on the angular power spectrum. The non-Gaussianity found in the other two (adjacent) pointings seems to be associated to a local deviation of the power spectrum of these fields with respect to the common power spectrum of the complete data set, at angular scales of the third acoustic peak (ℓ = 700–900). No evidence of residual systematics is found in this case, and unsubtracted point sources are not a plausible explanation either. If those visibilities are removed, the differences of the new power spectrum with respect to the published one only affect three bins. A cosmological analysis based on this new VSA power spectrum alone shows no differences in the parameter constraints with respect to our published results, except for the physical baryon density, which decreases by 10 per cent. Finally, the method has been also used to analyse the VSA observations in the Corona Borealis supercluster region. Our method finds a clear deviation (99.82 per cent) with respect to Gaussianity in the second-order moment of the distribution, and which cannot be explained as systematic effects. A detailed study shows that the non-Gaussianity is produced in scales of ℓ ≈ 500, and that this deviation is intrinsic to the data (in the sense that cannot be explained in terms of a Gaussian field with a different power spectrum). This result is consistent with the Gaussianity studies in the Corona Borealis data presented in Génova-Santos et al. which show a strong decrement that cannot be explained as primordial CMB.

Additional Information

© 2006 The Authors. Journal compilation © 2006 RAS. Accepted 2006 March 17. Received 2006 February 9; in original form 2005 November 4. Published: 26 May 2006. We thank the staff of the Mullard Radio Astronomy Observatory, the Jodrell Bank Observatory and the Teide Observatory for invaluable assistance in the commissioning and operation of the VSA. The VSA is supported by PPARC and the IAC. Partial financial support was provided by the Spanish Ministry of Science and Technology project AYA2001-1657. We also acknowledge the Spanish project ESP2004-07067-C03-01.

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August 19, 2023
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