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

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 $zsimeq 0.14$, 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 10s 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, $gtrsim 5 sigma$ and $gtrsim 6 sigma$, respectively, for the two fiducial radii. The line-of-sight position of the deepest region of the void is $zsimeq 0.15-0.25$. Our data, combined with an earlier measurement by Granett et al. 2010, are consistent with a large $R_{rm void}=(220 pm 50) h^{-1}Mpc $ supervoid with $delta_{m} simeq -0.14 pm 0.04$ centered at $z=0.22pm0.03$. Such a supervoid, constituting at least a $simeq 3.3sigma$ fluctuation in a Gaussian distribution of the $Lambda CDM$ model, is a plausible cause for the Cold Spot.