EXPANDING HYDRODYNAMICAL JETS CROSSING A GALACTIC HALO INTERGALACTIC MEDIUM INTERFACE

We have performed two-dimensional hydrodynamical simulations of axisymmetric, initially conical, jets with parameters that are reasonable for radio sources. The initial propagation is through isothermal (T ∼ 107 K) galactic halos with power-law density distributions. The jets then emerge across a pressure-matched interface into a hotter but less dense medium, with parameters characteristic of an intracluster or intergalactic gas. Within the halo the jets retain roughly constant opening angles and velocities and the mean jet density declines nearly in tandem with the halo density. The rate of advance of the bow shock and working surface rises for steep power-laws, b ≡ -d ln ρ/d ln R > 2, but declines for shallow ones (b < 2). Upon crossing the interface the jets accelerate and are eventually focused toward cylindrical shapes with long but narrow cocoons. The strongest internal shock - a reconfinement shock - is usually in the vicinity of the interface. If the density drop is large enough the originally light beam can emerge as denser than the outer external medium and will then propagate nearly ballistically with essentially no cocoon. Comparisons are made with earlier simulations of jets through constant density external media and with analytical models which have been useful in reproducing statistical properties of powerful radio sources.