Alignment of quasar polarizations with large-scale structures^⋆,⋆⋆

¹ Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, B5c, 4000 Liège, Belgium
e-mail: hutsemekers@astro.ulg.ac.be
² Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany

Received: 18 July 2014
Accepted: 7 September 2014

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 on 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.