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We apply spherical needlets to the Wilkinson Microwave Anisotropy Probe5-year cosmic microwave background (CMB) dataset, to search for imprints ofnon-isotropic features in the CMB sky. We use the needlets localizationproperties to resolve peculiar features in the CMB sky and to study how thesefeatures contribute to the anisotropy power spectrum of the CMB. In addition tothe now well-known "cold spot" of the CMB map in the southern hemisphere, wealso find two hot spots at greater than 99% confidence level, again in thesouthern hemisphere and closer to the Galactic plane. While the cold spotcontributes to the anisotropy power spectrum in the multipoles between l=6 tol=33, the hot spots are found to be dominating the anisotropy power in therange between l=6 and l=18. Masking both the cold and the two hot spots resultsin a reduction by about 15% in the amplitude of the angular power spectrum ofCMB around l=10. The resulting changes to the cosmological parameters when thepower spectrum is estimated masking these features (in addition to the WMAPteam's KQ85 mask) are within the 1$\sigma$ errors published with the WMAP maskonly. We also study the asymmetry between the angular power spectra evaluatedon the northern and southern hemispheres. When the features detected byneedlets are masked, we find that the difference in the power, measured interms of the anisotropy variance between l=4 and l=18, is reduced by a factor2. We make available a mask related to needlet features for more detailedstudies on asymmetries in the CMB anisotropy sky.

Needlet Detection of Features in WMAP CMB Sky and the Impact on Anisotropies and Hemispherical Asymmetries