Correlated orientations of the axes of large quasar groups on Gpc scales
Abstract
Correlated orientations of quasar optical and radio polarization, and of radio jets, have been reported on Gpc scales, possibly arising from intrinsic alignment of spin axes. Optical quasar polarization appears to be preferentially either aligned or orthogonal to the host largescale structure, specifically large quasar groups (LQGs). Using a sample of 71 LQGs at redshifts 1.0 ≤ z ≤ 1.8, we investigate whether LQGs themselves exhibit correlated orientation. We find that LQG position angles (PAs) are unlikely to be drawn from a uniform distribution (pvalues 0.008 ≲ p ≲ 0.07). The LQG PA distribution is bimodal, with median modes at $\bar{\theta }\sim 45\pm 2^{\circ }, 136\pm 2^{\circ }$, remarkably close to the mean angles of quasar radio polarization reported in two regions coincident with our LQG sample. We quantify the degree of alignment in the PA data, and find that LQGs are aligned and orthogonal across very large scales. The maximum significance is $\simeq 0.8{{\ \rm per\ cent}}$ (2.4σ) at typical angular (proper) separations of ~30° (1.6 Gpc). If the LQG orientation correlation is real, it represents largescale structure alignment over scales larger than those predicted by cosmological simulations and at least an order of magnitude larger than any so far observed, with the exception of quasarpolarization/radiojet alignment. We conclude that LQG alignment helps explain quasarpolarization/radiojet alignment, but raises challenging questions about the origin of the LQG correlation and the assumptions of the concordance cosmological model.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 April 2022
 DOI:
 10.1093/mnras/stac269
 arXiv:
 arXiv:2201.11474
 Bibcode:
 2022MNRAS.511.4159F
 Keywords:

 methods: statistical;
 surveys;
 quasars: general;
 largescale structure of Universe;
 cosmology: observations;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 Accepted for MNRAS