# Evidence against a supervoid causing the CMB Cold Spot

## TL;DR

This study investigates whether a supervoid could explain the CMB Cold Spot and finds that the observed voids are too small and insufficient to account for the Cold Spot via the ISW effect, suggesting a primordial origin.

## Contribution

The paper provides the first detailed galaxy redshift survey of the Cold Spot region, demonstrating that voids are too small to explain the Cold Spot through the ISW effect, challenging the supervoid hypothesis.

## Key findings

- Void sizes are too small to explain the Cold Spot via ISW effect.
- The Cold Spot's galaxy distribution resembles control fields without temperature decrements.
- Results suggest a primordial origin for the Cold Spot rather than line-of-sight effects.

## Abstract

We report the results of the 2dF-VST ATLAS Cold Spot galaxy redshift survey (2CSz) based on imaging from VST ATLAS and spectroscopy from 2dF AAOmega over the core of the CMB Cold Spot. We sparsely surveyed the inner 5$^{\circ}$ radius of the Cold Spot to a limit of $i_{AB} \le 19.2$, sampling $\sim7000$ galaxies at $z<0.4$. We have found voids at $z=$ 0.14, 0.26 and 0.30 but they are interspersed with small over-densities and the scale of these voids is insufficient to explain the Cold Spot through the $\Lambda$CDM ISW effect. Combining with previous data out to $z\sim1$, we conclude that the CMB Cold Spot could not have been imprinted by a void confined to the inner core of the Cold Spot. Additionally we find that our 'control' field GAMA G23 shows a similarity in its galaxy redshift distribution to the Cold Spot. Since the GAMA G23 line-of-sight shows no evidence of a CMB temperature decrement we conclude that the Cold Spot may have a primordial origin rather than being due to line-of-sight effects.