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Correlated orientations of quasar optical and radio polarisation, and ofradio jets, have been reported on Gpc scales, possibly arising from intrinsicalignment of spin axes. Optical quasar polarisation appears to bepreferentially either aligned or orthogonal to the host large-scale structure,specifically large quasar groups (LQGs). Using a sample of 71 LQGs at redshifts$1.0 \leq z \leq 1.8$, we investigate whether LQGs themselves exhibitcorrelated orientation. We find that LQG position angles (PAs) are unlikely tobe drawn from a uniform distribution ($p$-values $0.008 \lesssim p \lesssim0.07$). The LQG PA distribution is bimodal, with median modes at$\bar{\theta}\sim45\pm2^{\circ}, 136\pm2^{\circ}$, remarkably close to the meanangles of quasar radio polarisation reported in two regions coincident with ourLQG sample. We quantify the degree of alignment in the PA data, and find thatLQGs are aligned and orthogonal across very large scales. The maximumsignificance is $\simeq 0.8\%$ ($2.4\sigma$) at typical angular (proper)separations of $\sim 30^{\circ}$ (1.6 Gpc). If the LQG orientation correlationis real, it represents large-scale structure alignment over scales larger thanthose predicted by cosmological simulations and at least an order of magnitudelarger than any so far observed, with the exception of quasar-polarisation /radio-jet alignment. We conclude that LQG alignment helps explainquasar-polarisation / radio-jet alignment, but raises challenging questionsabout the origin of the LQG correlation and the assumptions of the concordancecosmological model.

Correlated orientations of the axes of large quasar groups on Gpc scales