Velocity and confinement of large-scale jets

I consider several issues connected with the velocities and confinement properties of kpc-scale jets in FRII sources. There is considerable evidence that large-scale jets are at least mildly relativistic. I discuss whether the Doppler-beaming interpretation of one-sidedness can be reconciled with Barthel s unified scheme, and consider modifications to the Doppler beaming formula due to the directionality of the magnetic field. The synchrotron-emitting regions of many FRII jets appear to be overpressured with respect to their surroundings, and yet seem to be effectively confined. I consider several possible confinement mechanisms, and discuss the implications of a small volume filling factor in the synchrotron emissivity. Finally, I argue that most lobe asymmetry could be due to environmental effects, and show that even a small asymmetry in the ambient intergalactic medium can lead to a large asymmetry in lobe/core separation.