Precessing jets and molecular outflows: A 3D numerical study

We present 3D numerical hydrodynamical simulations of precessing supersonic heavy jets to explore their evolution, how they differ from straight jets, and how well they serve as a model for generating molecular outflows from young stellar objects (YSOs). The dynamics are studied with a number of high-resolution simulations on a Cartesian grid (128 × 128 × 128 zones) using a high-order finite difference method. A range of cone angles and precession rates are included in the study. Two higher resolution runs (256 × 256 × 256 zones) were made for comparison in order to confirm numerical convergence of global flow characteristics. Morphological, kinematical and dynamical characteristics of precessing jets are described, and compared to important properties of straight jets and also to observations of YSOs. In order to examine the robustness of precessing jets as a means of producing molecular outflows around YSOs, 'synthetic observations' of the momentum distributions of the simulated precessing jets are compared to observations of molecular outflows. It is found that precessing jets match better the morphology, highly forward-driven momentum and momentum distributions along the long axis of molecular outflows than do wind-driven or straight jet-driven flow models.