The central engines of radio-quiet quasars

Two rival hypotheses have been proposed for the origin of the compact radio flux observed in radio-quiet quasars (RQQs). It has been suggested that the radio emission in these objects, typically some two or three orders of magnitude less powerful than in radio-loud quasars (RLQs), either represents emission from a circumnuclear starburst or is produced by radio jets with bulk kinetic powers similar to 10(3) times lower than those of RLQs with similar luminosity ratios in other wavebands. We describe the results of high-resolution (similar to pc-scale) radio-imaging observations of a sample of 12 RQQs using the Very Long Baseline Array (VLBA). We find strong evidence for jet-producing central engines in eight members of our sample.