Numerical study of the Kelvin-Helmholtz instability and its effect on synthetic emission from magnetized jets

Abstract

Context. Nonthermal emission from active galactic nucleus (AGN) jets extends up to large scales, even though they are prone to many magnetohydrodynamic instabilities. Aims. The main focus of this study is to understand the effect of magnetohydrodynamic instabilities on the nonthermal emission from large-scale AGN jets. Methods. We performed high-resolution three-dimensional numerical magnetohydrodynamic simulations of a plasma column to investigate the dynamical and emission properties of jet configurations at kiloparsec scales with different magnetic field profiles, jet speeds, and density contrast. We also obtained synthetic nonthermal emission signatures for different viewing angles using an approach that assumes static particle spectra and that is obtained by evolving the particle spectra using Lagrangian macroparticles incorporating the effects of shock acceleration and radiative losses. Results. We find that shocks due to the Kelvin-Helmholtz (KH) instability in the axial magnetic field configurations can strongly affect the jet dynamics. Additionally, we also find weak biconical shocks in the underdense jet columns. The helical magnetic field hinders the vortex growth at the shear surface and thereby stabilizes the jet column. With the evolving particle spectra approach, the synthetic spectral energy distributions obtained for cases with strong KH instability show multiple humps ranging from the radio to the TeV gamma-ray band. Conclusions. We conclude that high-energy electrons that are accelerated in the vicinity of freshly formed shocks due to KH instability result in high X-ray emission.