Correlations between multiple tracers of the cosmic web

TL;DR

This paper investigates correlations between different cosmic web tracers, revealing that apparent signals are often due to selection biases or chance alignments, and reports a new alignment of large quasar groups with potential cosmological implications.

Contribution

It provides a critical re-analysis of previous CMB-SNe correlations and introduces the first evidence of large quasar groups' coherent alignment at high redshift.

Findings

CMB-SNe correlation likely due to selection bias

Detected alignment of LQGs at ~2.4 sigma significance

LQG orientations correlate with quasar polarization angles

Abstract

The large-scale structure of the Universe is a cosmic web of interconnected clusters, filaments, and sheets of matter. This PhD comprises two complementary projects investigating the cosmic web using correlations between three different tracers: the cosmic microwave background (CMB), supernovae (SNe), and large quasar groups (LQGs). In the first project we re-analyse the apparent correlation between CMB temperature and SNe redshift reported by Yershov, Orlov and Raikov. They presented evidence that the WMAP/Planck CMB pixel-temperatures at SNe locations tend to increase with increasing redshift. They suggest this could be caused by the Integrated Sachs-Wolfe effect and/or by residual foreground contamination. Our analysis supports the prima facie existence of the correlation but attributes it instead to a composite selection bias caused by the chance alignment of seven deep survey fields with CMB hotspots. These seven fields contain just 9.2% of the SNe sample. We estimate the likelihood of their falling on CMB hotspots by chance is approximately 1 in 11. In the second project we investigate for the first time the apparent coherent alignment of LQGs in the redshift range 1.0 <= z <= 1.8. We find that the position angles (PAs) of LQGs are correlated, specifically aligned and orthogonal, with a maximum significance of ~2.4 sigma at typical angular (comoving) separations of ~30 degrees (~1.6 Gpc). Spatial coincidence between our LQG sample and regions of quasar polarization alignment first reported by Hutsemekers, and the similarity between LQG PAs and radio polarization angles reported by Pelgrims and Hutsemekers, suggest an interesting result.