Could multiple voids explain the Cosmic Microwave Background Cold Spot anomaly?

TL;DR

This paper investigates whether multiple cosmic voids along the line of sight can explain the Cold Spot anomaly in the CMB, using simulations of void arrangements and their ISW+RS effects.

Contribution

It introduces multi-void models with different configurations to assess their ability to replicate the Cold Spot and reduce its tension with the LCDM model.

Findings

Multiple void configurations can produce Cold Spot-like profiles.

Closely placed low-redshift voids are effective in mimicking the Cold Spot.

Removing Cold Spot-like profiles reduces tension with the LCDM model.

Abstract

Understanding the observed Cold Spot (CS) (temperature of ~ -150 mu K at its centre) on the Cosmic Microwave Background (CMB) is an outstanding problem. Explanations vary from assuming it is just a > 3 sigma primordial Gaussian fluctuation to the imprint of a supervoid via the Integrated Sachs-Wolfe and Rees-Sciama (ISW+RS) effects. Since single spherical supervoids cannot account for the full profile, the ISW+RS of multiple line-of-sight voids is studied here to mimic the structure of the cosmic web. Two structure configurations are considered. The first, through simulations of 20 voids, produces a central mean temperature of ~-50 mu K. In this model the central CS temperature lies at ~ 2 sigma but fails to explain the CS hot ring. An alternative multi-void model (using more pronounced compensated voids) produces much smaller temperature profiles, but contains a prominent hot ring. Arrangements containing closely placed voids at low redshift are found to be particularly well suited to produce CS-like profiles. We then measure the significance of the CS if CS-like profiles (which are fitted to the ISW+RS of multi-void scenarios) are removed. The CS tension with the LCDM model can be reduced dramatically for an array of temperature profiles smaller than the CS itself.