UNIFIED SCHEMES FOR ACTIVE GALAXIES - A CLUE FROM THE MISSING FANAROFF-RILEY TYPE-I QUASAR POPULATION

We link the lack of FR I type structure among quasars to the void of r adio loud quasars below a critical disk luminosity of similar to 10(46 ) erg/sec in the PG sample. We argue that the opening angle of the obs curing torus in radio loud quasars depends on the power of the central engine, approaching the jet's beaming angle near the FR I/FR II break . Consequently, low power radio quasars would either be classified as radio galaxies (FRI) or strongly core-boosted (BL Lac) object, dependi ng on the aspect angle, and no conspicuous transitional population wou ld be expected for FR I sources. A closing torus with decreasing power would not only obscure the optical nucleus for most aspect angles but would also enhance the entrainment of the cool torus material into th e jet stream, causing obscuration along the jet's periphery, as well a s the et's deceleration to form a FR I source. Above a critical lumino sity, the wider torus allows for FR II type jets and visibility of the nuclear optical emission, characteristic of radio loud quasars. Appar ently, at the same engine power the torus opening in radio weak quasar s and Seyferts is substantially wider than in radio loud quasars, prob ably because of different dynamics or feeding mechanisms in disk and e lliptical galaxies. This provides a clue for the radio-loud/radio-quie t dichotomy of quasars if the the jet/torus interaction leads to injec tion of relativistic e+/- via pp collisions. Strong jet/torus interact ion may lead to a substantial injection of secondary pairs and collima tion in radio loud quasars, while weak interaction in radio weak quasa rs leads neither to pair injection nor to good collimation.