Very long baseline interferometry at a wavelength of 3.4 mm

Abstract

In recent years the angular distribution of intensity of the compact cores of quasars and radio galaxies has been mapped in detail by very long baseline interferometry (VLBI) arrays^1,2. These observations have shown that asymmetric radio structure is common in active nuclei³, and that a high proportion of the brightest sources exhibit superluminal motion^4,5. The sources generally have an elongated structure, or jet, which dominates at long centimetre wavelengths, and a compact core at one end of the jet which dominates at short centimetre wavelengths. The association of the core components with the shortest wavelengths, and the most compact features, leads us to link core radiation with the unidentified central engines in these energetic systems. We report here the first detection of interference fringes by VLBI at a wavelength of 3.4 mm (89 GHz). The success of these observations demonstrates the feasibility of millimetre VLBI and opens this important wavelength range to mapping with a resolution of 10⁻⁴ arc s. The compact radio source in the nucleus of 3C84 (NGC1275) was observed for a 9-h period on the 485-km (1.4 × 10⁸ λ) baseline between the Owens Valley Radio Observatory and the Hat Creek Observatory. These observations show that the structure is more compact at 89 GHz than at 22 GHz.