Could multiple voids explain the cosmic microwave background Cold Spot anomaly?

Abstract

Understanding the observed Cold Spot (CS, temperature of ~-150 μK at its centre) on the cosmic microwave background is an outstanding problem. Explanations vary from assuming it is just a ≳3σ 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 μK. In this model the central CS temperature lies at ~2σ but fails to explain the CS hot ring. An alternative multivoid 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 multivoid scenarios) are removed. The CS tension with the λ cold dark matter model can be reduced dramatically for an array of temperature profiles smaller than the CS itself.