MERLIN observations of superluminal radio sources

Hybrid radio maps of nine superluminal extragalactic radio sources and the core-dominated quasar 4C 39.25 are presented which were made with the Jodrell Bank Multi-element Radio Linked Interferometer Network (MERLIN) at frequencies of 408 and/or 1666 MHz. The superluminal sources include seven quasars (NRAO 140, 3C 179, 3C 273, 3C 279, 3C 345, 3C 446, and 3C 454.3), the Seyfert Type I galaxy 3C 120, and BL Lac; all the sources except 3C 179 are of the flat-spectrum core-dominated 2type. The suggestion is made that flat-spectrum core-dominated sources and steep-spectrum normal double sources are closely related. It is shown that extended structure surrounds the cores of most superluminal sources and that the properties of the extended structure are consistent with a unified scheme in which the core-dominated sources have a relativistic jet directed toward the observer.