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 ～ 10³ times lower than those of RLQs with similar luminosity ratios in other wavebands. We describe the results of high-resolution (～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.