Conclusion: Crossing the FR I/FR II Division

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11. Conclusion: Crossing the FR I/FR II Division  

We seem to be approaching another ``unified scheme"-for the dynamics of energy transport in FR I and FR II sources. In this scheme, FR I jets decelerate rapidly  in the cores of elliptical galaxies, dissipating some bulk energy into internal heat and rapid spreading.  FR II jets avoid this fate, leaving the galactic cores at higher Mach numbers, remaining better collimated, and perhaps preserving a ``hidden'' high-velocity  spine  until the hot spots. This picture accounts for many basic intensity and polarimetric properties of both types of jet, and may also be the key to understanding relationships between jets and hot spots in FR II sources. The root question of what determines the shape of the radio luminosity function  and the relative numbers of FR I and FR II  sources remains open. FR II galaxies have more luminous emission-line systems than FR I's (e.g., Baum, Zirbel, & O'Dea 1995), but the optical distinctions between radio-quiet and radio loud FR I galaxies are evaporating in the face of larger samples (Ledlow & Owen, these Proceedings).

Alan Bridle
Wed Apr 10 10:19:46 EDT 1996