Are Cluster Radio Relics Revived Fossil Radio Cocoons?

Abstract

A new model for the, so called, `cluster radio relics' is presented (Ensslin & Gopal-Krishna 2000). Fossil radio cocoons, resulting from the former activity of radio galaxies, should contain a low energy relativistic electron population and magnetic fields. Electrons with an age of even up to 2 Gyr can be re-accelerated adiabatically to radio emitting energies, if the fossil radio plasma gets compressed in an environmental shock wave. Such a wave can be caused by a merging event of galaxy clusters, or by the accretion onto galaxy clusters. An implication of this model is the existence of a population of diffuse, ultra-steep spectrum, very low-frequency radio sources located inside and possibly outside of clusters of galaxies, tracing the revival of aged fossil radio plasma by the shock waves associated with large-scale structure formation.

4 pages, 2 figures, uses newpasp.sty (included) and epsf.sty. To appear in R.A. Laing and K.M. Blundell (Eds.) 'Particles and Fields in Radio Galaxies' Oxford, UK, 2000, to be published by the Astronomical Society of the Pacific (ASP)