The Red Radio Ring: a gravitationally lensed hyperluminous infrared radio galaxy at z=2.553 discovered through the citizen science project SPACE WARPS

International audience; We report the discovery of a gravitationally lensed hyperluminous infrared galaxy (intrinsic L-IR approximate to 10(13) L-circle dot) with strong radio emission (intrinsic L-1.4 GHz approximate to 10(25) WHz(-1)) at z = 2.553. The source was identified in the citizen science project SPACE WARPS through the visual inspection of tens of thousands of iJK(s) colour composite images of luminous red galaxies (LRGs), groups and clusters of galaxies and quasars. Appearing as a partial Einstein ring (r(e) approximate to 3 arcsec) around an LRG at z = 0.2, the galaxy is extremely bright in the sub-millimetre for a cosmological source, with the thermal dust emission approaching 1 Jy at peak. The redshift of the lensed galaxy is determined through the detection of the CO(3 -\textgreater 2) molecular emission line with the Large Millimetre Telescope's Redshift Search Receiver and through [O III] and Ha line detections in the near-infrared from Subaru/Infrared Camera and Spectrograph. We have resolved the radio emission with high-resolution (300-400 mas) eMERLIN L-band and Very Large Array C-band imaging. These observations are used in combination with the near-infrared imaging to construct a lens model, which indicates a lensing magnification of mu approximate to 10. The source reconstruction appears to support a radio morphology comprised of a compact (\textless250 pc) core and more extended component, perhaps indicative of an active nucleus and jet or lobe.