Galaxy Counts on the CMB Cold Spot

TL;DR

This study investigates the Cold Spot in the CMB to determine if a supervoid causes it, using galaxy counts and redshift data, and finds no significant supervoid evidence.

Contribution

The paper provides the first detailed galaxy count analysis in the Cold Spot region, ruling out a large supervoid as the cause of the Cold Spot.

Findings

No 100 Mpc supervoid with delta=-0.3 at 0.5<z<0.9 detected.

Fluctuations consistent with cosmic variance, not a supervoid.

Voids smaller than 50 Mpc have minor impact on CMB temperature.

Abstract

The Cold Spot on the Cosmic Microwave Background could arise due to a supervoid at low redshift through the integrated Sachs-Wolfe effect. We imaged the region with MegaCam on the Canada-France-Hawai'i Telescope and present galaxy counts in photometric redshift bins. We rule out the existence of a 100Mpc radius spherical supervoid with underdensity delta=-0.3 at 0.5<z<0.9 at high significance. The data are consistent with an underdensity at low redshift, but the fluctuations are within the range of cosmic variance and the low density areas are not contiguous on the sky. Thus, we find no strong evidence for a supervoid. We cannot resolve voids smaller than 50Mpc radius; however, these can only make a minor contribution to the CMB temperature decrement.