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