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

Kovács, András and García-Bellido, Juan (2016) Cosmic troublemakers: the Cold Spot, the Eridanus Supervoid, and the Great Walls. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 462 (2). pp. 1882-1893. ISSN 0035-8711

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Abstract

The alignment of the CMB Cold Spot and the Eridanus supervoid suggests a physi- cal 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 red- shift 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 mea- surements are consistent with a central matter underdensity δ0 ≈ −0.25, projected transverse radius r⊥ 0 ≈ 195 Mpc/h with an extra deepening in the centre, and line- of-sight radius r‖ 0 ≈ 500 Mpc/h, i.e. an ellipsoidal supervoid. The expected integrated Sachs-Wolfe imprint of such an elongated supervoid is at the ∆TISW ≈ −40μK level, thus inappropriate to accounting for the Cold Spot pattern in the CMB.

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