Intrinsic Origin Of Extreme-Scale Rotation Of Quasar Polarization Vectors

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.