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Probing non-Gaussianities in the CMB on an incomplete sky using surrogates

Probing non-Gaussianities in the CMB on an incomplete sky using surrogates

This video was recorded at NIPS Workshops, Sierra Nevada 2011. For investigations of CMB data sets, the analysis of Fourier phases has proven to be a useful method, since all potential higher order correlations, which directly point to non-Gaussianities, are contained in the phases and the correlations among them. The method of surrogate maps with shuffled Fourier phases represents one way of analysing the phases. The shuffling approach relies on the orthogonality of the spherical harmonics, which only holds for the full sky. However, astrophysical foreground emission, mainly present in the Galactic plane, are a major challenge in CMB analyses. We demonstrate the feasibility to generate surrogates by Fourier-based methods also for an incomplete data set by transforming the spherical harmonics into a new set of basis functions that are orthonormal on the cut sky. The results show that non-Gaussianities and hemispherical asymmetries in the CMB as identified in several former investigations, can still be detected even when the complete Galactic plane is removed. We conclude that the Galactic plane cannot be the dominant source for these anomalies.


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