RAD@home discovery of extragalactic radio rings and odd radio circles: clues to their origins

ABSTRACT We present three rare and striking extragalactic radio sources discovered through visual inspection of low-frequency continuum maps from LoTSS DR2 and TGSS by the RAD@home citizen-science collaboratory. The first, RAD J131346. 9+500320, is the first clear Odd Radio Circle (ORC) identified in LoTSS. At z ₏₇₎ₓ 0. 94, it hosts a pair of intersecting rings of 300 kpc diameter, embedded in diffuse emission extending over 800 kpc, making it both the most distant and most powerful ORC reported to date. Its steep spectrum (₅₄^144=1. 22 0. 15) points to a relic synchrotron origin. The second object, RAD J122622. 6+640622, is a 865 kpc giant radio galaxy whose southern jet is abruptly deflected, inflating a 100 kpc limb-brightened ring, while the northern jet terminates in a compact hotspot-like feature. The third, RAD J142004. 0+621715 (440 kpc), shows a comparable ring at the end of its northern filamentary jet, along with a secondary filament parallel to its southern jet. All three systems lie in 10^14\, M_ clusters or group-scale haloes, suggesting that environmental density gradients and possible jet–galaxy interactions play a central role in shaping these ring morphologies. These discoveries expand the zoo of extragalactic radio morphologies, highlight the diversity of pathways that can generate ring-like synchrotron structures, and demonstrate the continuing importance of human pattern recognition in identifying rare sources that escape current automated pipelines.