Searching for Extremal Spots in Planck Lensing Maps

TL;DR

This paper searches for extremal spots in Planck 2018 CMB lensing maps using multi-scale wavelet analysis, finding no significant deviations from Gaussian expectations.

Contribution

It introduces a multi-scale, multi-filter wavelet analysis to identify extremal features in CMB lensing maps, extending previous Cold Spot studies.

Findings

No significant extremal features detected after analysis.

Lensing maps are statistically consistent with Gaussian simulations.

Initial hints of spots at small scales were not statistically significant.

Abstract

A great deal of attention has been given to the so-called Cold Spot in maps of the cosmic microwave background (CMB) temperature. We present a similar analysis, searching for extremal spots in the CMB lensing convergence and lensing potential maps from the Planck 2018 data release. We perform a multi-scale and multi-filter analysis using the first three members of the Mexican-hat wavelet family to search for extremal features of different shapes and sizes. Although an initial analysis appears to show the existence of some extremal spots at scales below about 5 degree, we conclude, after marginalising over all scales and filters, that no significant features are detected in the lensing maps. We conclude that in terms of maxima and minima of various sizes, the lensing data have similar statistical properties to Gaussian simulations.