Making Fanaroff-Riley I radio sources

III. The effects of the magnetic field on relativistic jets’ propagation and source morphologies^⋆

¹ Dipartimento di Fisica, Università degli Studi di Torino, Via Pietro Giuria 1, 10125 Torino, Italy
e-mail: silvano.massaglia@unito.it
² INAF/Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy

Received: 23 June 2020
Accepted: 11 December 2021

Abstract

Extragalactic radio sources appear under different morphologies, the most frequent ones are classified as Fanaroff-Riley type I (FR I), typically with lower luminosities, and Fanaroff-Riley type II, (FR II), typically more luminous. This simple classification, however, has many exceptions that we intend to investigate. Following previous analyses in the three-dimensional Hydrodynamic and Magneto-Hydrodynamic limits, we extend the numerical investigation to the Relativistic Magneto-Hydrodynamic regime, to include sources whose jet kinetic power sets in the range that separates FR Is from FR IIs. We consider weakly and mildly relativistic, underdense, supersonic jets that propagate in a stratified medium. In the model, the ambient temperature increases with distance from the jet origin maintaining constant pressure. We present three cases with low, high and intermediate kinetic luminosity that evolve into different morphologies. We find that the resulting morphology can be highly time dependent and that, apart from the jet power, the jet-to-ambient density ratio and the magnetization parameter play a crucial role in the jet evolution as well.