AND ASTROPHYSICS Letter to the Editor

Abstract. So far all relativistically boosted jets with superlumi-nal motion have only been detected in typical radio galaxies with early type host galaxies. We have now discovered superluminal motion in the Seyfert I galaxy III Zw 2, classied as a spiral. Su-perluminal motion was rst inferred from the spectral evolution of the source and then conrmed by VLBI observations. The lower limit for the apparent expansion speed is 1:25 0:09 c. The fact that the spectral and spatial evolution are closely linked demonstrates that we are dealing with real physical expansion. Prior to this rapid expansion we have seen a period of virtually no expansion with an expansion speed less than 0.04 c. Since III Zw 2 is also part of a sample of so called radio-intermediate quasars (RIQ), it conrms earlier predictions of superluminal motion for this source, based on the argument that RIQs could be relativistically boosted jets in radio-weak quasars and Seyfert galaxies