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

TL;DR

This study investigates hemispherical power asymmetries in WMAP 7-year temperature and polarization maps, finding temperature asymmetry consistent with prior results and no significant polarization asymmetry, while also forecasting Planck's detection potential.

Contribution

It extends previous asymmetry analyses to polarization data and introduces an optimal estimator for all six CMB spectra, assessing asymmetries across the sky.

Findings

Temperature asymmetry aligns with previous findings.

No significant polarization asymmetry detected.

Method forecasts Planck's ability to detect dipole modulation.

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.