Too few spots in the cosmic microwave background

TL;DR

This paper examines the scarcity of large-scale hot and cold spots in the WMAP-5 CMB data, revealing significant discrepancies with Gaussian LCDM simulations and highlighting the impact of the low quadrupole on these anomalies.

Contribution

It provides the first detailed analysis of large-scale spot counts in WMAP-5 data, showing fewer spots than predicted by Gaussian LCDM models and emphasizing the role of the low quadrupole.

Findings

Fewer large-scale spots in observed CMB than in simulations.

Low mean temperature fluctuation on 4-8 degree scales.

Low quadrupole significantly affects spot count discrepancies.

Abstract

We investigate the abundance of large-scale hot and cold spots in the WMAP-5 temperature maps and find considerable discrepancies compared to Gaussian simulations based on the LCDM best-fit model. Too few spots are present in the reliably observed cosmic microwave background (CMB) region, i.e., outside the foreground-contaminated parts excluded by the KQ75 mask. Even simulated maps created from the original WMAP-5 estimated multipoles contain more spots than visible in the measured CMB maps. A strong suppression of the lowest multipoles would lead to better agreement. The lack of spots is reflected in a low mean temperature fluctuation on scales of several degrees (4 to 8), which is only shared by less than 1% (0.16%-0.62%) of Gaussian LCDM simulations. After removing the quadrupole, the probabilities change to 2.5%-8.0%. This shows the importance of the anomalously low quadrupole for the statistical significance of the missing spots. We also analyze a possible violation of Gaussianity or statistical isotropy (spots are distributed differently outside and inside the masked region).