# Extragalactic Radio Sources and the WMAP Cold Spot

## TL;DR

This study links the WMAP cold spot to a large, empty cosmic void at moderate redshift, showing a significant dip in extragalactic source brightness and counts, challenging standard cosmological models.

## Contribution

It provides evidence that the WMAP cold spot is caused by a large void at z<=1, connecting CMB anomalies with large-scale structure and reducing the need for non-Gaussian early universe explanations.

## Key findings

- Detected a 20-45% dip in NVSS sources at the cold spot location.
- The dip correlates with the WMAP cold spot, suggesting a physical connection.
- A ~140 Mpc empty void at z<=1 can explain the cold spot's properties.

## Abstract

We detect a dip of 20-45% in the surface brightness and number counts of NVSS sources smoothed to a few degrees at the location of the WMAP cold spot. The dip has structure on scales of approximately 1-10 degrees. Together with independent all-sky wavelet analyses, our results suggest that the dip in extragalactic brightness and number counts and the WMAP cold spot are physically related, i.e., that the coincidence is neither a statistical anomaly nor a WMAP foreground correction problem. If the cold spot does originate from structures at modest redshifts, as we suggest, then there is no remaining need for non-Gaussian processes at the last scattering surface of the CMB to explain the cold spot. The late integrated Sachs-Wolfe effect, already seen statistically for NVSS source counts, can now be seen to operate on a single region. To create the magnitude and angular size of the WMAP cold spot requires a ~140 Mpc radius completely empty void at z<=1 along this line of sight. This is far outside the current expectations of the concordance cosmology, and adds to the anomalies seen in the CMB.