Time-dependent radio emission from evolving jets

TL;DR

This study uses hydrodynamic simulations and radiative transfer calculations to analyze the time-dependent radio emission from evolving jets in various ambient media, revealing environmental influences on jet morphology and emission features.

Contribution

It introduces a comprehensive modeling approach combining hydrodynamics and radiative transfer to study jet evolution and environmental effects on radio emission in AGN.

Findings

Emission intensity and size depend on jet evolution stages.

Environmental interactions influence jet features like shocks and hotspots.

Derived relations help constrain AGN jet hydrodynamics and ambient medium structure.

Abstract

We investigated the time-dependent radiative and dynamical properties of light supersonic jets launched into an external medium, using hydrodynamic simulations and numerical radiative transfer calculations. These involved various structural models for the ambient media, with density profiles appropriate for galactic and extragalactic systems. The radiative transfer formulation took full account of emission, absorption, re-emission, Faraday rotation and Faraday conversion explicitly. High time-resolution intensity maps were generated, frame-by-frame, to track the spatial hydrodynamical and radiative properties of the evolving jets. Intensity light curves were computed via integrating spatially over the emission maps. We apply the models to jets in active galactic nuclei (AGN). From the jet simulations and the time-dependent emission calculations we derived empirical relations for the emission intensity and size for jets at various evolutionary stages. The temporal properties of jet emission are not solely consequences of intrinsic variations in the hydrodynamics and thermal properties of the jet. They also depend on the interaction between the jet and the ambient medium. The interpretation of radio jet morphology therefore needs to take account of environmental factors. Our calculations have also shown that the environmental interactions can affect specific emitting features, such as internal shocks and hotspots. Quantification of the temporal evolution and spatial distribution of these bright features, together with the derived relations between jet size and emission, would enable us to set constraints on the hydrodynamics of AGN and the structure of the ambient medium.