III Zw 2, the first superluminal jet in a Seyfert galaxy

So far all relativistically boosted jets with superluminal 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, c lassified as a spiral. Superluminal motion was first inferred from the spec tral evolution of the source and then confirmed by VLBI observations. The l ower limit for the apparent expansion speed is 1.25 +/- 0.09 c. The fact th at 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 les s than 0.04 c. Since III Zw 2 is also part of a sample of so called radio-i ntermediate quasars (RIQ), it confirms earlier predictions of superluminal motion for this source, based on the argument that RIQs could be relativist ically boosted jets in radio-weak quasars and Seyfert galaxies.