The alignment of distant radio sources

Abstract

The relative orientation of the axes of extragalactic extended radio sources was first investigated by Willson, who noted that in the 3CR sample there was a tendency for the axes to lie parallel to each other for sources separated by ≤10° on the sky. Using two larger samples, Sanders has recently concluded that this tendency to align is present at a high confidence level (>3 σ) only for distant (redshift, z>0.4) sources and could arise from gravitational lensing by superclusters, if most of the matter in a closed universe is in thin filaments. Because of the important cosmological implications, we have now attempted to verify the effect using two more independent and larger source samples and find no significant tendency for axis alignment. In view of this negative result, we also investigated a sample formed by adding well-observed radio quasars to 3CR sources (similar to one of the two samples used by Sanders) and found that, even in this sample, the effect shows up only at a marginally significant level (<2 σ).