Intrinsic Origin Of Extreme-Scale Rotation Of Quasar Polarization Vectors

TL;DR

This paper proposes a physical explanation for the large-scale rotation of quasar polarization vectors, linking it to magnetic field transformations in accretion disks and their alignment over cosmological timescales.

Contribution

It introduces analytical models of polarization evolution in magnetized accretion disks and connects magnetic field transformations to observed polarization rotations at cosmological scales.

Findings

Analytical expressions for polarization degree and angle in accretion disks.

Possible explanation for half of the observed polarization rotation.

Mechanism linking magnetic field evolution to polarization vector alignment.

Abstract

Extreme-scale alignment of quasar optical polarization vectors at cosmological scales ($z\le 2$) is also characterized by the rotation of mean position angle $\chi$ with $\Delta \chi \approx 30^{\circ}$ per 1 Gpc. For observing interval of $z$ the total rotation angle acquires the value $\sim 90^{\circ}$. We suggest the possible explanation of the half of this rotation as a consequence of physical transformation of initially vertical magnetic field ${\bf B}_{\|}$, directed along the normal ${\bf N}$ to the surface of accretion disk, into the horizontal (perpendicular to ${\bf N}$) one. We found asymptotical analytical expressions for axially averaged polarization degree $p$ and mean position angle $\chi$ for various types of magnetized accretion disks. We found also that during the evolution can be realized the case $B_{\bot}\approx B_{\|}$ where position angle $\chi$ rotates from $45^{\circ}$ to zero. This rotation may occur during fairly great cosmological time (corresponding to $\Delta z\sim 1-2$). The part of rotation $\sim \Delta \chi \approx 45^{\circ}$ can be explained by a mechanism of alignment of polarization vectors, say distribution of the part of quasars as a spiral in the cosmic space with slow variation of rotation axis of corresponding accretion disks. Both mechanisms are mutually related one with another.