Evidence against a supervoid causing the CMB Cold Spot

Ruari Mackenzie,Peder Norberg,Istvan Szapudi,Malcolm N Bremer,András Kovács,Yan-Chuan Cai,Madusha L P Gunawardhana,Tom Shanks

doi:10.1093/mnras/stx931

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.

Highlights

The Cosmic Microwave Background (CMB) provides the earliest snapshot of the evolution of the Universe
We report the results of the 2dF-VLT Survey Telescope (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 find that our ‘control’ field Galaxy And Mass Assembly (GAMA) G23 shows a similarity in its galaxy redshift distribution to the Cold Spot

Summary

Introduction

The Cosmic Microwave Background (CMB) provides the earliest snapshot of the evolution of the Universe. The CMB Cold Spot is an ∼ 5◦ radius, -150 μK feature in the CMB in the Southern Hemisphere which represents a departure arising in between < 0.2% (Cruz et al 2005) to < 1 − 2% (Planck Collaboration et al 2016b) Gaussian simulations. It consists of a cold 5◦ radius core surrounded by a less extreme 10◦ radius halo. The Cold Spot is surrounded by a high temperature ring which is important for its original detection using a Spherical Mexican Hat Wavelet (SMHW)

Results

Discussion

Conclusion