The radio structure of 3C 316, a galaxy with double-peaked narrow optical emission lines

The galaxy 3C 316 is the brightest in the radio band among the optically selected candidates exhibiting double-peaked narrow optical emission lines. Observations with the Very Large Array, Multi-Element Remotely Linked Interferometer Network (e-MERLIN), and the European Very Long Baseline Interferometry Network (EVN) at 5 GHz have been used to study the radio structure of the source in order to determine the nature of the nuclear components and to determine the presence of radio cores. The e-MERLIN image of 3C 316 reveals a collimated coherent east-west emission structure with a total extent of about 3 kpc. The EVN image shows seven discrete compact knots on an S-shaped line. However, none of these knots could be unambiguously identified as an active galactic nucleus (AGN) core. The observations suggest that the majority of the radio structure belongs to a powerful radio AGN, whose physical size and radio spectrum classify it as a compact steep-spectrum source. Given the complex radio structure with radio blobs and knots, the possibility of a kpc-separation dual AGN cannot be excluded if the secondary is either a naked core or radio quiet.