Highly-magnified, multiply-imaged radio counterparts of the sub-mm starburst emission in the cluster-lens MS0451.6-0305

Context. Previous authors have reported the detection of intrinsically faint sub-mm emission lensed by the cluster MS0451.6-0305. They suggest that this emission arises from a merging system composed of a Ly-break galaxy and a pair of extremely red objects which are multiply-imaged in the optical/NIR observations. Aims. Since the submm emission presents an unusually large angular extent (similar to 1'), the possible radio emission asociatted with that system can help to identify optical/NIR counterparts due to the higher spatial resolution and astrometric accuracy of the radio observations. Methods. Archive VLA data (BnA configuration at 1.4 GHz) was reduced and analysed. A simple lens model was constructed to aid the interpretation of the radio and pre-existing sub-mm and optical/NIR data. Results. We present a 1.4 GHz map of the central region of MS0451.6-0305 and report the detection of gravitationally lensed radio emission, coincident with the previously discovered sub-mm lensed emission. The overall morphology and scale of the radio and sub-mm emission are strikingly similar, extending (similar to 1') across the sky. This observation strongly suggests that the radio and sub-mm emission arise from the same sources. Preliminary estimates of the total S-850 (mu m)/S (1.4 GHz) flux density ratio appear to be consistent with that expected from distant star forming galaxies. The radio emission is resolved into 7 distinct components, and the overall structure can be explained, using a simple lens model, with three multiply-imaged radio sources at z similar to 2.9. One of these sources is predicted to lie in the middle of the previously mentioned merging system in the source plane, suggesting that it is related to the intense star formation generated during the merging process.