Hemispherical power asymmetries in the WMAP 7-year low-resolution temperature and polarization maps

Abstract: We test the hemispherical power asymmetry of the WMAP 7-year low-resolution temperature and polarization maps. We consider two natural estimators for such an asymmetry and exploit our implementation of an optimal angular power spectrum estimator for all the six CMB spectra. By scanning the whole sky through a sample of 24 directions, we search for asymmetries in the power spectra of the two hemispheres, comparing the results with Monte Carlo simulations drawn from the WMAP 7-year best-fit model. Our analysis extends previous results to the polarization sector. The level of asymmetry on the ILC temperature map is found to be compatible with previous results, whereas no significant asymmetry on the polarized spectra is detected. Moreover, we show that our results are only weakly affected by the a posteriori choice of the maximum multipole considered for the analysis. We also forecast the capability to detect dipole modulation by our methodology at Planck sensitivity.