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

TL;DR

This study maps the Eridanus supervoid in 3D using galaxy catalogues, revealing an elongated, complex structure that is unlikely to fully explain the CMB Cold Spot via the integrated Sachs-Wolfe effect.

Contribution

It provides a detailed 3D analysis of the Eridanus supervoid, uncovering its substructure and large-scale shape, and assesses its impact on the CMB Cold Spot.

Findings

The Eridanus supervoid is an elongated, ellipsoidal structure with significant substructure.

The supervoid's ISW imprint is insufficient to explain the Cold Spot.

Large-scale structures like superclusters are identified as potential compensations for the matter deficit.

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 cata\-logues 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 $\delta_0 \approx -0.25$, projected transverse radius $r_{0}^{\perp}\approx 195$ Mpc/h with an extra deepening in the centre, and line-of-sight radius $r_{0}^{\parallel}\approx500$ Mpc/h, i.e. an ellipsoidal supervoid. The expected integrated Sachs-Wolfe imprint of such an elongated supervoid is at the $\Delta T_{\rm ISW} \approx -40 \mu K$ level, thus inappropriate to accounting for the Cold Spot pattern in the CMB.