Alignment of quasar polarizations with large-scale structures

TL;DR

This study finds that quasar polarization vectors are aligned with large-scale structures at z ~ 1.3, suggesting quasar spin axes tend to be parallel to these cosmic structures, based on polarization and emission line width correlations.

Contribution

First observational evidence linking quasar polarization orientations with large-scale cosmic structures at high redshift.

Findings

Polarization vectors are aligned with large-scale structures.

Quasars with perpendicular polarization have broader emission lines.

Quasar spin axes are likely parallel to large-scale structures.

Abstract

We have measured the optical linear polarization of quasars belonging to Gpc-scale quasar groups at redshift z ~ 1.3. Out of 93 quasars observed, 19 are significantly polarized. We found that quasar polarization vectors are either parallel or perpendicular to the directions of the large-scale structures to which they belong. Statistical tests indicate that the probability that this effect can be attributed to randomly oriented polarization vectors is of the order of 1%. We also found that quasars with polarization perpendicular to the host structure preferentially have large emission line widths while objects with polarization parallel to the host structure preferentially have small emission line widths. Considering that quasar polarization is usually either parallel or perpendicular to the accretion disk axis depending on the inclination with respect to the line of sight, and that broader emission lines originate from quasars seen at higher inclinations, we conclude that quasar spin axes are likely parallel to their host large-scale structures.