Searching for planar signatures in WMAP

TL;DR

This study investigates planar deviations in WMAP CMB data using angular-planar statistics, revealing anomalies likely caused by residual foreground contamination and highlighting the importance of foreground removal procedures.

Contribution

The paper applies a novel angular-planar statistical method to WMAP data, analyzing the impact of foreground cleaning and masking on detected anisotropies in the CMB.

Findings

Full-sky maps show anomalies at (l,ell)=(2,5),(4,7),(6,8) due to residual foregrounds.

Masked maps reveal anomalies at (10,8) and (2,9), suggesting foreground cleaning may hide or create anomalies.

A persistent anomaly at (10,5) indicates possible residual contamination aligned with the galaxy's plane.

Abstract

We search for planar deviations of statistical isotropy in the Wilkinson Microwave Anisotropy Probe (WMAP) data by applying a recently introduced angular-planar statistics both to full-sky and to masked temperature maps, including in our analysis the effect of the residual foreground contamination and systematics in the foreground removing process as sources of error. We confirm earlier findings that full-sky maps exhibit anomalies at the planar ($l$) and angular ($\ell$) scales $(l,\ell)=(2,5),(4,7),$ and $(6,8)$, which seem to be due to unremoved foregrounds since this features are present in the full-sky map but not in the masked maps. On the other hand, our test detects slightly anomalous results at the scales $(l,\ell)=(10,8)$ and $(2,9)$ in the masked maps but not in the full-sky one, indicating that the foreground cleaning procedure (used to generate the full-sky map) could not only be creating false anomalies but also hiding existing ones. We also find a significant trace of an anomaly in the full-sky map at the scale $(l,\ell)=(10,5)$, which is still present when we consider galactic cuts of 18.3% and 28.4%. As regards the quadrupole ($\ell=2$), we find a coherent over-modulation over the whole celestial sphere, for all full-sky and cut-sky maps. Overall, our results seem to indicate that current CMB maps derived from WMAP data do not show significant signs of anisotropies, as measured by our angular-planar estimator. However, we have detected a curious coherence of planar modulations at angular scales of the order of the galaxy's plane, which may be an indication of residual contaminations in the full- and cut-sky maps.