Power asymmetries in the cosmic microwave background temperature and polarization patterns

Abstract

We test the asymmetry of the cosmic microwave background anisotropy jointly in temperature and polarization. We study the hemispherical asymmetry, previously found only in the temperature field, with respect to the axis identified by Hansen et al. To this extent, we make use of the low-resolution Wilkinson Microwave Anisotropy Probe 5-yr temperature and polarization Nside= 16 maps and our implementation of an optimal power spectrum estimator. We consider two simple estimators for the power asymmetry and we compare our findings with Monte Carlo simulations which take into account the full noise covariance matrix. We confirm an excess of power in temperature angular power spectrum in the Southern hemisphere at a significant level, between 3 σ and 4 σ depending on the exact range of multipoles considered. We do not find significant power asymmetry in the gradient (curl) component EE (BB) of polarized angular spectra. Furthermore, cross-correlation power spectra, i.e. TE, TB, EB, show no significant hemispherical asymmetry. We also show that the cold spot found by Vielva et al. in the Southern Galactic hemisphere does not alter the significance of the hemispherical asymmetries on multipoles which can be probed by maps at resolution Nside= 16. Although the origin of the hemispherical asymmetry in temperature remains unclear, the study of the polarization pattern could add useful information on its explanation. We therefore forecast by Monte Carlo the Planck capabilities in probing polarization asymmetries.