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Two-dimensional, high-resolution numerical simulations are performed for hydrodynamical jets and are followed for times greater than in previous simulations. The jet parameters are chosen so as to give good fits to extragalactic radio sources, and these new simulations correspond to lifetimes over 10$^8$yr and yield jets extending to several hundred kpc. In all these simulations initially conical jets first propagate through isothermal (T$\approx$10$^7$K) atmospheres of active galaxies whose densities decline as power-laws, and then cross into an even hotter, but less dense, intracluster medium, whereupon they accelerate and collimate. Here we confirm results of earlier simulations of these circumstances and also explore the relatively minor effects of variations in the steepness of the interface gradients in temperature and density.
A key new result of these lengthy simulations is that these collimated beams eventually suffer Kelvin-Helmholtz type instabilities, which, in conjunction with strong internal shocks, can effectively choke the flow of plasma into the jet head, so that the outer part of the jet separates into a slowly expanding plasmoid. But as long as the jet remains fed from the nucleus, a second Mach disk and working surface, corresponding to a new hot-spot and lobe, will form. These phenomena could explain the morphology of some extended sources with current hot spots far inside their extended lobe emission.
This work is supported in part by NSF grant AST91-02106.
