On the deceleration of Fanaroff-Riley Class I jets: mass loading of magnetized jets by stellar winds.

Abstract

In this paper we present steady-state RMHD simulations that include a mass-load term to study the process of jet deceleration. The mass-load mimics the injection of a proton-electron plasma from stellar winds within the host galaxy into initially pair plasma jets, with mean stellar mass-losses ranging from 10−14 to 10−9 M⊙ yr−1. The spatial jet evolution covers ∼500 pc from jet injection in the grid at 10 pc from the jet nozzle. Our simulations use a relativistic gas equation of state and a pressure profile for the ambient medium. We compare these simulations with previous dynamical simulations of relativistic, non-magnetised jets. Our results show that toroidal magnetic fields can prevent fast jet expansion and the subsequent embedding of further stars via magnetic tension. In this sense, magnetic fields avoid a runaway deceleration process. Furthermore, when the mass-load is large enough to increase the jet density and produce fast, differential jet expansion, the conversion of magnetic energy flux into kinetic energy flux (i.e., magnetic acceleration), helps to delay the deceleration process with respect to non-magnetised jets. We conclude that the typical stellar population in elliptical galaxies cannot explain jet deceleration in classical FRI radio galaxies. However, we observe a significant change in the jet composition, thermodynamical parameters and energy dissipation along its evolution, even for moderate values of the mass-load.

Ambilateral collimation study of the twin-jets in NGC 1052

“…On the other hand, emission from the disk wind itself might contribute to the imaged radiation, which has the potential to prevent us from detecting the true, intrinsic jet structure. Furthermore, deviations of the apparent opening angle and width with frequency upstream of the break point can be explained by differential expansion, which is required by magnetic acceleration (Vlahakis & Königl 2004;Komissarov et al 2009;Komissarov 2012;Anglés-Castillo et al 2021). Therefore, as we identify the region of differential expansion with the upstream jets at distances 10 4 R S , we expect the jet acceleration to take place in that region.…”

Accretion mode versus radio morphology in the LOFAR Deep Fields

“…The primary source of material to be entrained is thought to be the central hot-gas environment, rather than winds from young stellar populations (e.g. Laing & Bridle 2014;Anglés-Castillo et al 2021), though stellar mass loading can play an important role for weaker jets (Perucho et al 2014). For massive ellipticals, the typical hosts of radio-loud AGN, the hot-gas environment richness is expected to scale with galaxy mass (e.g.…”

Long-term FRII jet evolution in dense environments

“…In constrast, the large-scale morphologies of FRI jets are still difficult to recover from numerical simulations due to the long time-scales involved in their evolution, because they are slow and decollimated, so their expansion is much slower (see , for a simulation of the initial evolution of a FRI jet). The processes involved in jet deceleration and the energy dissipation at FRI jets should also be tackled in future work (e.g., Gourgouliatos & Komissarov 2018;Matsumoto & Masada 2019;Perucho 2020;Anglés-Castillo et al 2021).…”

“…At kiloparsec scales, extragalactic jets are mainly observed at radio frequencies, and show a morphological and brightness dichotomy between powerful sources showing bright hotspots and radio lobes, and less powerful radio sources that show irregular, decollimated structures, which was first noted by Fanaroff & Riley (1974). The main reason responsible for this dichotomy is probably jet power (Rawlings & Saunders 1991;Ghisellini & Celotti 2001), with a transition region in which the environmental properties and stellar populations may play a significant role (e.g., Kawakatu, Kino & Nagai 2009;Perucho 2019Perucho , 2020Anglés-Castillo et al 2021).…”