Interactions of a Light Hypersonic Jet with a Nonuniform Interstellar Medium

Abstract

We present three-dimensional simulations of the interaction of a light hypersonic jet with an inhomogeneous thermal and turbulently supported disk in an elliptical galaxy. These simulations are applicable to the GPS/CSS phase of extragalactic radio sources. The interstellar medium in these simulations consists of a conventional hot (T ∼ 104 K) component together with a warm (T ∼ 104 K) turbulently supported disk whose local density is described by a lognormal density distribution and whose spatial structure is realized from a fractal power law. We model the jet as a light, supersonic nonrelativistic flow with parameters selected to be consistent with a relativistic jet with kinetic power just above the FR1/FR2 break. We identify four generic phases in the evolution of such a jet with the inhomogeneous interstellar medium: (1) an initial "flood and channel" phase, where progress is characterized by high-pressure gas finding changing weak points in the ISM, flowing through channels that form and reform over time; (2) a spherical, energy-driven bubble phase, where the bubble is larger than the disk scale, but the jet remains fully disrupted close to the nucleus; (3) a subsequent, rapid, jet break-out phase where the jet breaks free of the last obstructing dense clouds, becomes collimated once more, and pierces the spherical bubble; and (4) a classical phase, where the jet propagates in a momentum-dominated fashion similar to jets in single-component hot halos, leading to the classical jet-cocoon-bow shock structure. Mass transport in the simulations is investigated, and we propose a model for the morphology and component proper motions in the well-studied compact symmetric object 4C 31.04.