Shocking news outside of cluster cores

TL;DR

This paper discusses the detection of low surface brightness radio sources in cluster outskirts, revealing new insights into cluster shocks, relics, and magnetic field measurements in large-scale structures.

Contribution

It introduces techniques for identifying faint radio sources and reports new observations of cluster shocks, relics, and magnetic field ambiguities in the context of low magnetic field environments.

Findings

Detection of cluster-like sources in poor environments.

Identification of a shock on the border of the Coma cluster halo.

Discovery of filamentary relics suggesting face-on emission.

Abstract

With magnetic fields below one microgauss, the minimum pressures of synchrotron plasmas start to approach those in the thermal gas in cluster outskirts and the more diffuse WHIM in large-scale structure filaments. We summarize some of our techniques to find the corresponding low surface brightness radio sources and what we have uncovered. We identify cluster-like sources in poor environments, likely requiring very efficient relativistic particle acceleration, as well as very diffuse radio galaxies with no indications of current activity. More detailed observations of Coma and a new radio-identified cluster highlight some emerging issues in cluster-related shocks: Coma has a shock on the border of its halo, suggesting a connection between the two; the Coma relic appears to be an "infall" shock, associated with a 500 km/s infalling column of galaxies; the new cluster has filamentary pieces in addition to its more classical halo and peripheral relics, suggesting that we are beginning to see relic emission face on. Finally, a different kind of shock comes from our recent finding of ambiguities in the determination of rotation measures which will influence cluster magnetic field studies.