Large-scale acoustic peak shift in the Planck CMB data

TL;DR

This paper analyzes the Planck CMB data to identify large-scale shifts in the angular power spectrum across the sky, revealing features like the Cold Spot and Draco supervoid, and detecting a dipole pattern.

Contribution

It introduces a method to compare small patch power spectra across the sky, visualizes the relative shifts, and analyzes their statistical properties, highlighting large-scale anomalies.

Findings

Large relative shifts near Cold Spot and Draco supervoid

Detection of a dipole pattern in the feature map

Discussion of potential causes including foregrounds and systematics

Abstract

Cosmic microwave background (CMB) temperature anisotropies encode the history of the universe, which manifest itself in the angular power spectrum. We test the angular power spectra of small patches from the ESA $\textit{Planck}$ data. Known variations in the power spectra from small patches reveal informative details such as the gravitational lensing and the Doppler boosting effect. We compute the relative shifts of power spectra via comparing patches selected randomly from the CMB. We visualize the relative shifts on a full-sky HEALPix grid (a feature map) and analyze the statistical properties on the full-sky map. We find the regions contain the Cold Spot and the Draco supervoid have large relative shifts to large scales. We also find a dipole on the generated feature map comparing with simulations. We discuss possible ways to resolve this dipole on the feature map, including foregrounds, solar dipole systematics, and the uncertainty in our method.