Detection of a Supervoid Aligned with the Cold Spot of the Cosmic Microwave Background

Abstract

We use the WISE-2MASS infrared galaxy catalog matched with Pan-STARRS1 (PS1) galaxies to search for a supervoid in the direction of the Cosmic Microwave Background Cold Spot. Our imaging catalog has median redshift $z\simeq 0.14$, and we obtain photometric redshifts from PS1 optical colours to create a tomographic map of the galaxy distribution. The radial profile centred on the Cold Spot shows a large low density region, extending over 10's of degrees. Motivated by previous Cosmic Microwave Background results, we test for underdensities within two angular radii, $5^{\circ }$, and $15^{\circ }$. The counts in photometric redshift bins show significantly low densities at high detection significance, $\gtrsim 5\ddot{I}ƒ$ and $\gtrsim 6\ddot{I}ƒ$, respectively, for the two fiducial radii. The line-of-sight position of the deepest region of the void is $z\simeq 0.15-0.25$. Our data, combined with an earlier measurement by Granett et al. 2010, are consistent with a large $R_{\mathrm{void}}=(220\pm 50)h^{-1}Mpc$ supervoid with $\hat{I}{´}_m\simeq -0.14\pm 0.04$ centered at $z=0.22\pm 0.03$. Such a supervoid, constituting at least a $\simeq 3.3\ddot{I}ƒ$ fluctuation in a Gaussian distribution of the $\hat{I}›CDM$ model, is a plausible cause for the Cold Spot.

8 pages, 6 figures, accepted for publication by MNRAS