Cosmic troublemakers: the Cold Spot, the Eridanus supervoid, and the Great Walls

Abstract

The alignment of the CMB Cold Spot and the Eridanus supervoid suggests a physical connection between these two relatively rare objects. We use galaxy catalogues with photometric (2MPZ) and spectroscopic (6dF) redshift measurements, supplemented by low-redshift compilations of cosmic voids, in order to improve the 3D mapping of the matter density in the Eridanus constellation. We find evidence for a supervoid with a significant elongation in the line of sight, effectively spanning the total redshift range z < 0.3. Our tomographic imaging reveals important substructure in the Eridanus supervoid, with a potential interpretation of a long, fully connected system of voids. We improve the analysis by extending the line-of-sight measurements into the antipodal direction that interestingly crosses the Northern Local Supervoid at the lowest redshifts. Then it intersects very rich superclusters like Hercules and Corona Borealis, in the region of the Coma and Sloan Great Walls, as a possible compensation for the large-scale matter deficit of Eridanus. We find that large-scale structure measurements are consistent with a central matter underdensity δ₀ ≈ -0.25, projected transverse radius r₀^{perp }≈ 195 Mpc h^-1 with an extra deepening in the centre, and line-of-sight radius r₀^{allel }≈ 500 Mpc h^-1, I.e. an ellipsoidal supervoid. The expected integrated Sachs-Wolfe imprint of such an elongated supervoid is at the ΔT_ISW ≈ -40 μK level, thus inappropriate to accounting for the Cold Spot pattern in the CMB.