TEST OF UNIFIED SCHEMES USING JET OPENING ANGLES

Unified schemes attempt to classify radio loud quasars and Fanaroff-Ri ley Class II radio galaxies as a single type of object, whose properti es depend on the orientation of the jet axis relative to the line of s ight. We describe a new test of such unification schemes using observe d jet opening angles as orientation indicators and apply it to existin g data. Opening angles were measured for a subset of the 3CR catalogue , consisting of all identified extragalactic sources with P178 MHz> 10 (25) W/Hz and for which high resolution radio maps were found. This pr ovided a sample relatively free of orientation effects. The observed d istributions of opening angles for the quasars were compared with thos e of the galaxies, and with Monte Carlo simulations. We find that the observed jet opening angles of quasars tend to be larger than those of the galaxies; this result is consistent with, and supports, the unifi ed scheme. Detailed Monte Carlo simulations suggest the observations a re inconsistent with a simple unified scheme where a single orientatio n angle sharply distinguishes between quasars and galaxies. We modify Barthel's [ApJ, 336, 606 (1989)] unification scheme by introducing a r ange of orientation angles that differentiate quasars from galaxies; t his yields more consistent results. However, neither Barthel's unifica tion, nor the modification presented here, are fully able to account f or the observed differences in quasar and galaxy redshift distribution s. Finally, we demonstrate the existence of a loose anticorrelation be tween jet opening angle and source linear size, confirming that these parameters are useful as orientation indicators.