4C 18.68: A QSO with Precessing Radio Jets?

Extract

The radio source 4C 18.68, identified with the 16.5 m QSO 2305+187 (z = 0.313), was observed at 20 cm and 6 cm with the VLA in its highest-resolution configuration (A) on April 25, 1981, as part of a programme to map the radio structure of quasars for which optical structure has been mapped using the Canada-France-Hawaii telescope. The radio structure is remarkable, showing complex, curved structure at 6 cm resolution embedded in a halo ∼ 60 kpc across (H_O = 100 km/sec/Mpc, q_O = 0) seen most clearly in the 20 cm map. The polarisation is low (∼ 8% maximum at 6 cm) and follows the curved structure quite closely, showing the magnetic field direction to be along the curved structure. The central source has a flat spectrum, while the spectrum of the structure generally steepens with distance from the centre.