The evolution of slab jets and self-similar models of extragalactic radio sources

Abstract

Simple general arguments suggest that, like round jets, initially divergent hypersonic slab jets propagating through a uniform atmosphere are eventually recollimated by the high pressure of their cocoons and the subsequent evolution is approximately self-similar. Although slab jets are not directly relevant to astrophysical jets, they allow us to study the effects of enforced symmetry without resorting to expensive three-dimensional numerical simulations. In this paper we show that, although both jets with enforced mirror symmetry and those without eventually become self-similar, the flow depends significantly on the symmetry. In particular, the aspect ratio of the cocoon created by asymmetric jets seems to be independent of the initial jet opening angle for small opening angles, contrary to what is found for symmetric jets. This suggests that the hydrodynamics of the jet and its cocoon is much more complicated than has been assumed in current theoretical models of extragalactic radio sources and that results of two-dimensional axisymmetric numerical simulations can be rather misleading.