Distribution of Faraday Rotation Measure in Jets from Active Galactic Nuclei. II. Prediction from Our Sweeping Magnetic Twist Model for the Wiggled Parts of Active Galactic Nucleus Jets and Tails

Abstract

Distributions of Faraday rotation measure (FRM) and the projected magnetic field derived by a three-dimensional simulation of MHD jets are investigated based on our "sweeping magnetic twist model." FRM and Stokes parameters were calculated to be compared with radio observations of large-scale wiggled AGN jets on kiloparsec scales. We propose that the FRM distribution can be used to discuss the three-dimensional structure of the magnetic field around jets and the validity of existing theoretical models, together with the projected magnetic field derived from Stokes parameters. In a previous paper we investigated the basic straight part of AGN jets by using the result of a two-dimensional axisymmetric simulation. The derived FRM distribution has a general tendency to have a gradient across the jet axis, which is due to the toroidal component of the magnetic field generated by the rotation of the accretion disk. In this paper we consider the wiggled structure of the AGN jets by using the result of a three-dimensional simulation. Our numerical results show that the distributions of FRM and the projected magnetic field have a clear correlation with the large-scale structure of the jet itself, namely, three-dimensional helix. Distributions, seeing the jet from a certain direction, show a good matching with those in a part of the 3C 449 jet. This suggests that the jet has a helical structure and that the magnetic field (especially the toroidal component) plays an important role in the dynamics of the wiggle formation because it is due to a current-driven helical kink instability in our model.