Local anomalies around the third peak in the CMB angular power spectrum of the WMAP 7-year data

TL;DR

This study analyzes the WMAP 7-year data to identify localized anomalies in the CMB power spectrum around the third peak, revealing significant north-south asymmetries at high Galactic latitudes likely influenced by instrument noise.

Contribution

It provides the first detailed localized analysis of CMB power spectrum anomalies around the third peak using WMAP data, highlighting potential instrumental noise effects.

Findings

Significant north-south anomaly at high Galactic latitudes near the third peak

Anomalies are weaker in regions with higher observation counts, indicating noise influence

Opposite anomalies observed at low Galactic latitudes, possibly due to galactic contamination

Abstract

We estimate the power spectra of CMB temperature anisotropy in localized regions on the sky using the WMAP 7-year data. Here, we report that the north hat and the south hat regions at the high Galactic latitude (|b| >= 30 deg) show anomaly in the power spectrum amplitude around the third peak, which is statistically significant up to 3 sigma. We try to figure out the cause of the observed anomaly by analyzing the low Galactic latitude (|b|< 30 deg) regions where the galaxy contamination is expected to be stronger, and regions that are weakly or strongly dominated by the WMAP instrument noise. We also consider the possible effect of unresolved radio point sources. We found another but less statistically significant anomaly in the low Galactic latitude north and south regions whose behavior is opposite to the one at the high latitude. Our analysis shows that the observed north-south anomaly at high latitude becomes weaker on the regions with high number of observations (weak instrument noise), suggesting that the anomaly is significant at sky regions that are dominated by the WMAP instrument noise. We have checked that the observed north-south anomaly has weak dependences on the bin-width used in the power spectrum estimation and the Galactic latitude cut. We have also discussed the possibility that the detected anomaly may hinge on the particular choice of the multipole bin around the third peak. We anticipate that the issue of whether the anomaly is intrinsic one or due to the WMAP instrument noise will be resolved by the forthcoming Planck data.