Large-scale alignment of optical polarizations from distant QSOs using coordinate-invariant statistics

Abstract

We introduce several coordinate-invariant statistical procedures in order to test for alignment of polarizations of electromagnetic radiation from astrophysical sources. A large-scale alignment of optical polarizations from distant quasi-stellar objects (QSOs) has recently been observed by Hutsemékers and collaborators. The new statistical procedures are based on comparing polarizations at different angular coordinates by making a parallel transport. The results of these statistical procedures continue to support the existence of the large-scale alignment effect in the QSO optical polarization data. The alignment is found to be much more pronounced in the data sample with low degrees of polarization, p ≤ 2 per cent. This suggests that the alignment may be attributed to some propagation effect. The distance scale over which the alignment effect is dominant is found to be of order 1 Gpc. We also find that a very large-scale alignment is present in the large-redshift, z ≥ 1, data sample. In fact, the data sample with z ≥ 1 appears to be aligned over the entire celestial sphere. This alignment is seen independent of the degree of polarization of the sources. We discuss possible physical effects, such as extinction and pseudoscalar-photon mixing, which may be responsible for the observations.