Asymmetry of the CMB map: local and global anomalies

We investigate the sources of parity asymmetry in the CMB temperature maps using a pixel domain approach. We demonstrate that this anomaly is mainly associated with the presence of two pairs of high asymmetry regions. The first pair of peaks with Galactic coordinates (l, b) = (212 degrees,-21 degrees) and (32 degrees, 21 degrees) is associated with the Northern Galactic Spur and the direction of the dipole modulation of the power spectrum of the CMB anisotropy. The other pair ((l, b) = (332 degrees,-8 degrees) and (152 degrees, 8 degrees)) is located within the Galactic plane (the Galactic Cold Spot and its antipodal partner). Similar asymmetric peaks, but with smaller amplitudes, belong to the WMAP/Planck Cold Spot and its partner in the Northern Galactic Spur. These local anomalies increase the odd-multipole power to a level consistent with Gaussian simulations. In contrast, the deficit of symmetric peaks is accompanied by a deficit in the even-multipole power and is the source of the parity asymmetry of the CMB temperature maps at the level of about 3 sigma. We also evaluate the influence of the quadrupole, which is another source of the even-multipole deficit. If the low quadrupole is an intrinsic feature of the theoretical model, it will reduce the significance of the parity asymmetry to around the 2 sigma level. We also investigate the relationship between the asymmetry of the power spectrum and the level of the parity asymmetry in the framework of a model with dipole modulation of a statistically uniform Gaussian signal. We show that these two anomalies are innately linked to each other.

Automated summary

By using a pixel domain approach, we investigated the sources of parity asymmetry in the CMB temperature maps and found that they are mainly related to the presence of two pairs of high asymmetry regions. The asymmetric peaks in the Galactic plane and the Northern Galactic Spur lead to an increase in odd-multipole power, while the deficit of symmetric peaks is associated with a deficit in the even-multipole power, resulting in parity asymmetry of the CMB temperature maps.