A redshift survey towards the CMB Cold Spot

TL;DR

This study conducted a redshift survey towards the CMB Cold Spot to investigate if a large void could explain its origin, finding no evidence of such a void on large scales but identifying smaller scale structures.

Contribution

The paper provides the first detailed redshift distribution analysis towards the Cold Spot, challenging the void hypothesis for its cause.

Findings

No large void detected at 0.35<z<1.

Small-scale redshift gaps observed, but not uniquely indicative of voids.

Redshift distribution similar to control samples, suggesting no anomaly.

Abstract

We have carried out a redshift survey using the VIMOS spectrograph on the VLT towards the Cosmic Microwave Background cold spot. A possible cause of the cold spot is the Integrated Sachs-Wolfe effect imprinted by an extremely large void (hundreds of Mpc in linear dimension) at intermediate or low redshifts. The redshift distribution of over seven hundred z<1 emission-line galaxies drawn from an I-band flux limited sample of galaxies in the direction of the cold spot shows no evidence of a gap on scales of Delta-z> 0.05 as would be expected if such a void existed at 0.35<z<1. There are troughs in the redshift distribution on smaller scales (Delta-z ~0.01) indicating that smaller scale voids may connect regions separated by several degrees towards the cold spot. A comparison of this distribution with that generated from similarly-sized subsamples drawn from widely-spaced pointings of the VVDS survey does not indicate that the redshift distribution towards the cold spot is anomalous or that these small gaps can be uniquely attributed to real voids.