Speaker
Description
Radio observations of restarted jets in active galaxies reveal complex morphologies and spectral signatures that trace episodic jet activity. We investigate these phenomena using high-resolution 3D simulations with the PLUTO code, combined with Lagrangian macroparticles to model non-thermal electrons. This framework enables spatially resolved modelling of synchrotron emission, spectral index, and polarization over a broad range of radio frequencies. Our simulations show that, after jet shutdown, cocoon emission fades rapidly. When the jet restarts, it propagates through the cavity left by the previous activity, producing new compact emission within the older diffuse cocoon. We find that the main particle acceleration sites depend on jet power and magnetization, with forward shocks dominating in some cases and internal shocks in others. We find that the remnant cocoon conditions can disrupt the bow shock. We also identify new transient emission features when the restarted jet breaks out of the old cocoon. In addition, the new jet shows stronger depolarization than the old cocoon. The simulated emission, spectral index, and polarization maps closely resemble observations. These results provide new insights into jet duty cycles, particle acceleration, and radiative ageing in restarted radio galaxies.