Simulating the Enrichment of Fossil Radio Electrons by Multiple Radio Galaxies

We simulate the evolution of relativistic electrons injected into the intracluster medium by five radio galaxies. We study the spatial transport and the emission properties of the injected radio plasma over a ∼5 Gyr period, and the sequence of cooling and re-acceleration events experienced by electrons, using a Lagrangian approach joined with a numerical method to model the evolution of momentum spectra of relativistic electrons. When compared with electrons injected by shock waves, electrons injected by radio galaxies (here limited to a single injection event) in our tests are unable to fuel large ∼Mpc-sized radio relics with fossil electrons, as required by current theoretical models, while electrons previously seeded by other shocks can do this. On the other hand, the combination of seeding from radio galaxies and of re-acceleration events from plasma perturbation can produce detectable, small-scale, and filamentary emissions in the proximity (≤100–200 kpc) of radio galaxies.