Particle Rejuvenation In Distant Galaxy Clusters

© Francesco de Gasperin (Leiden University)

A composite (false-colour) image of the galaxy cluster Abell 1033. Optical light from individual galaxies, visible as coloured spots across the image, is obtained by the Sloan Digital Sky Survey, while in blue the X-ray emission observed with the Chandra satellite traces the hot gas. Radio emission from LOFAR and the VLA is shown in orange and traces a complex of radio sources including a tail of particles left behind by the galaxy moving towards the left of the image.

The steep spectrum emission in the central region of the cluster is detected only at the low frequencies to which LOFAR is sensitive. It is thought to have been perturbed and re-energised by the intracluster medium. Sources powered through this proposed mechanism can maintain electrons at higher energies than radiative aging would allow. If this mechanism is common for aged plasma, a population of mildly relativistic electrons can accumulate inside clusters and provide a seed population that can then be reaccelerated by shocks or turbulence to produce the cluster-wide emission that is observed in some massive merging clusters.