Echoes of the Dying Light: The Evolution and Spectral Signatures of Simulated Remnant Radio Galaxies

Abstract:

Radio galaxy remnants are the quiescent phase of radio-loud active galactic nuclei (RLAGN) and provide key insight into AGN duty cycles and feedback. Observationally, remnants are challenging to identify, as their spectral and morphological properties often overlap with active sources, necessitating multi-frequency data.

In my PhD, I worked on the largest suite (to-date) of three-dimensional hydrodynamic simulations of active and remnant RLAGN evolving in realistic environments. Using synthetic radio emission generated from these simulations, I investigated how jet power, environment, and active-phase duration shape the dynamics, spectral evolution, and observability of remnants. I showed that low-density environments delay the transition to buoyancy, and high-powered sources sustain forward shocks that continue heating their surroundings. I also find several trends in the spectral evolution of remnants that are dependent on environment properties.

I further explore remnant identification using machine learning on simulated radio data, finding that even simple models can distinguish active and remnant sources, though younger remnants are harder to classify. Finally, I introduce a new method to calculate radio and X-ray observables directly from simulations, enabling detailed, high-resolution studies of lobe emission and its interaction with the environment.

These results provide a theoretical framework to interpret current and upcoming low-frequency surveys and improve our understanding of the lifecycle and impact of RLAGN.

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