Non-Gaussianities in the local curvature of the 5-year WMAP data

Details Non-Gaussianities in the local curvature of the 5-year WMAP data Non-Gaussianities in the local curvature of the 5-year WMAP data

2010-02-09

arxiv.org/abs/1002.1811v2

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

7 pages, 6 figures, included test on weak lensing simulations

Scientific paper

Using the 5 year WMAP data, we re-investigate claims of non-Gaussianities and asymmetries detected in local curvature statistics of the 1 year WMAP data. In Hansen et al 2004, it was found that the northern ecliptic hemisphere was non-Gaussian at the ~1% level testing the densities of hill-, lake and saddle points based on the second derivatives of the CMB temperature map. The 5 year WMAP data has a much lower noise level and better control of systematics. Using these, we find that the anomalies are still present at a consistent level. Also the direction of maximum non-Gaussianity remains. Due to limited availability of computer resources, Hansen et al. 2004 were unable to calculate the full covariance matrix for the chi^2 test used. Here we apply the full covariance matrix instead of the diagonal approximation and find that the non-Gaussianities disappear and there is no preferred non-Gaussian direction. We compare with simulations of weak lensing to see if this may cause the observed non-Gaussianity when using diagonal covariance matrix. We conclude that weak lensing does not produce non-Gaussianity in the local curvature statistics at the scales investigated in this paper. The cause of the non-Gaussian detection in the case of a diagonal matrix remains unclear.

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