Diffuse Cluster-Like Radio Emission in Poor Environments

Abstract

We present a study of the spectral, polarimetric, morphological, and environmental properties of the diffuse radio source 0809+39 using observations taken with the Westerbork Synthesis Radio Telescope, the Very Large Array, and archival optical and X-ray data. The source has two distinct diffuse, steep-spectrum components, one in the north that is highly polarized, and a linear southern component undetected in polarization. We discuss several plausible origins for each component, and conclude that the northern bright polarized component is most likely a radio relic associated with a poor z ~ 0.2 cluster of galaxies, with a radio/X-ray luminosity ratio two orders of magnitude above typical values. The southern component is aligned with a more extended filament of galaxies ~5 Mpc long at z ~ 0.04. Deep optical and X-ray follow-ups are still needed in order to confirm and understand the physical origins of the synchrotron emission. Whatever the details of these origins, 0809+39 highlights the utility of synchrotron radiation for illuminating the diffuse components of low density environments unrelated to rich clusters.