Ray-tracing in relativistic jet simulations: A polarimetric study of magnetic field morphology and electron scaling relations

Abstract

Context. The jets emanating from the centers of active galactic nuclei are among the most energetic objects in the Universe. Investigating how the morphology of the jet's synchrotron emission depends on the magnetic nature of the jet's relativistic plasma is fundamental to the comparison between numerical simulations of relativistic jets and their observed polarization. Aims. Through the use of 3D relativistic magnetohydrodynamic jet simulations (computed using the PLUTO code) we study how the synchrotron emission from a jet depends on the morphology of its magnetic field structure. Through the application of polarized radiative transfer and ray-tracing (via the RADMC-3D code), we create synthetic radio maps of the total intensity of a jet as well as the linearly and circularly polarized intensity for each jet simulation. Methods. In particular, we create synthetic ray-traced images of the polarized synchrotron emission from a jet when this latter carries a predominantly poloidal, helical, and toroidal magnetic field. We also explore several scaling relations in which the underlying electron power-law distribution is set proportional to: (i) the jet's thermal plasma density, (ii) its internal energy density, and (iii) its magnetic energy density. Results. We find that: (i) the jet emission is edge-brightened when the magnetic field is toroidal in nature and spine brightened when the magnetic field is poloidal in nature; (ii) the circularly polarized emission exhibits both negative and positive sign for the toroidal magnetic field morphology at an inclination of i = 45° as well as i = 5°; and (iii) the relativistic jet's emission is largely independent of different emission scaling relations when the ambient medium is excluded.