On the formation of cluster radio relics

By Torsten A. Ensslin, M. Brueggen. 2001

142 citations recorded by the source corpus.

ABSTRA C T In several merging clusters of galaxies so-called cluster radio relics have been observed. These are extended radio sources which do not seem to be associated with any radio galaxies. Two competing physical mechanisms to accelerate the radio-emitting electrons have been proposed: (i) diffusive shock acceleration and (ii) adiabatic compression of fossil radio plasma by merger shock waves. Here the second scenario is investigated. We present detailed three-dimensional magneto-hydrodynamical simulations of the passage of a radio plasma cocoon filled with turbulent magnetic fields through a shock wave. Taking into account synchrotron, inverse Compton and adiabatic energy losses and gains, we evolved the relativistic electron population to produce synthetic polarization radio maps. On contact with the shock wave the radio cocoons are first compressed and finally torn into filamentary structures, as is observed in several cluster radio relics. In the synthetic radio maps the electric polarization vectors are mostly perpendicular to the filamentary radio structures. If the magnetic field inside the cocoon is not too strong, the initially spherical radio cocoon is transformed into a torus after the passage of the shock wave. Very recent, high-resolution radio maps of cluster radio relics seem to exhibit such toroidal geometries in some cases. This supports the hypothesis that cluster radio relics are fossil radio cocoons that have been revived by a shock wave. For a late-stage relic the ratio of its global diameter to the filament diameter should correlate with the shock strength. Finally, we argue that the total radio polarization of a radio relic should be well correlated with the three-dimensional orientation of the shock wave that produced the relic.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/9d2e6f3b7fede0255e4a768695a3863654d882cf

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Citations in the corpus

Constraining the population of cosmic ray protons in cooling flow clusters with γ-ray and radio observations: Are radio mini-halos of hadronic origin? (2003, background): “There is also evidence that reacceleration processes acting on fossil radio plasma produces small filamentary radio relics at the cluster periphery, so-called revived radio ghosts (Enßlin & Gopal-Krishna 2001; Enßlin & Br¨uggen 2002) presumably by adiabatic compression in shock waves.”
Diffuse Radio Emission from Galaxy Clusters (2019, background): “Due to the compression, the CR electrons in the cocoon regain energy boosting the radio synchrotron emission (Enßlin & Gopal-Krishna 2001; Enßlin & Brüggen 2002).”
Cosmic ray transport in galaxy clusters: implications for radio halos, gamma-ray signatures, and cool core heating (2010, background): “10 Radio phoenix in the taxonomy of Kempner et al. (2004): Enßlin & Gopal-Krishna (2001); Slee et al. (2001); Enßlin et al. (2001); Enßlin & Brüggen (2002); Kaiser & Cotter (2002); Brüggen et al. (2003); Gardini & Ricker (2004).”
Radio signature of cosmological structure formation shocks (2006, background): “…at the shock waves themselves (Enßlin et al. 1998; Miniati et al. 2001), or they could be old radio bubbles that are compressed by the passing shock wave and thus induced to emit observable synchrotron emission again (Enßlin & Gopal-Krishna 2001; Enßlin & Brüggen 2002; Hoeft et al. 2004).”
Heating Hot Atmospheres with Active Galactic Nuclei (2007, background): “This results in the formation of a vortex ring around the cavity after it has been overrun (Churazov et al. 2001; Enßlin & Brüggen 2002).”