Evidence presented by Yershov , Orlov and Raikov apparently showed that the WMAP / Planck cosmic microwave background ( CMB ) pixel-temperatures ( T ) at supernovae ( SNe ) locations tend to increase with increasing redshift ( z ) .
They suggest this correlation could be caused by the Integrated Sachs-Wolfe effect and/or by some unrelated foreground emission .
Here , we assess this correlation independently using Planck 2015 SMICA R2.01 data and , following Yershov et al. , a sample of 2783 SNe from the Sternberg Astronomical Institute .
Our analysis supports the prima facie existence of the correlation but attributes it to a composite selection bias ( high CMB T \times high SNe z ) caused by the accidental alignment of seven deep survey fields with CMB hotspots .
These seven fields contain 9.2 per cent of the SNe sample ( 256 SNe ) .
Spearman ’ s rank-order correlation coefficient indicates the correlation present in the whole sample ( \rho _ { s } = 0.5 , p-value = 6.7 \times 10 ^ { -9 } ) is insignificant for a sub-sample of the seven fields together ( \rho _ { s } = 0.2 , p-value = 0.2 ) and entirely absent for the remainder of the SNe ( \rho _ { s } = 0.1 , p-value = 0.6 ) .
We demonstrate the temperature and redshift biases of these seven deep fields , and estimate the likelihood of their falling on CMB hotspots by chance is at least \sim 6.8 per cent ( approximately 1 in 15 ) .
We show that a sample of 7880 SNe from the Open Supernova Catalogue exhibits the same effect and we conclude that the correlation is an accidental but not unlikely selection bias .