The CMB Derivatives of Planck's Beam Asymmetry

TL;DR

This paper analyzes how beam asymmetry and scanning strategy in Planck's CMB maps cause anisotropy, revealing a significant ecliptic latitude preference and exploring its implications for cosmic defect detection.

Contribution

It introduces a pixel space estimator for beam asymmetry effects and demonstrates their impact on CMB anisotropy analysis, aiding in the removal of such systematics.

Findings

Significant (~20 sigma) anisotropy aligned with ecliptic latitudes.

Scale dependence and morphology of the anisotropy characterized.

Simulation-based validation of anisotropy removal methods.

Abstract

We investigate the anisotropy in cosmic microwave background Planck maps due to the coupling between its beam asymmetry and uneven scanning strategy. Introducing a pixel space estimator based on the temperature gradients, we find a highly significant (~20 \sigma) preference for these to point along ecliptic latitudes. We examine the scale dependence, morphology and foreground sensitivity of this anisotropy, as well as the capability of detailed Planck simulations to reproduce the effect, which is crucial for its removal, as we demonstrate in a search for the weak lensing signature of cosmic defects.