The morphology and surface brightness of extragalactic jets.

A theoretical model of collimated jets in extragalactic radio sources is proposed. Recent laminar models are reviewed and shown to explain jet morphology but not the surface-brightness characteristics of the objects. The model proposed is based on an analogy to a laboratory jet and involves self-similar turbulent flow subject to intergalactic-medium entrainment. A mathematical description of sheared flow is developed; the mass, momentum, and energy-flux equations are integrated in a one-dimensional approach; particle-acceleration mechanisms are evaluated; the magnetic field is taken into account; solutions for the surface brightness are obtained; and synchrotron losses are considered. Numerical results for jets in NGC 315 and 3C-31 are presented graphically and found to be in reasonably good agreement with observations. The jet is seen as confined and slowing down in the first 100 arcsec and collimated by decreasing turbulence in the plateau region of the FWHM curve, with subsequent FWHM increase due to renewed turbulent entrainment and a slow decline in surface brightness.