Hydrodynamic simulations of molecular outflows driven by fast-precessing protostellar jets

Abstract

The structure of protostellar jets and outflows is determined by both the nature of the driving protostar and the enveloping environment. To deduce protostellar evolution from the outflow evolution, we need to distinguish between these influences. Here, we employ three-dimensional numerical simulations to investigate how outflow properties evolve as the jet direction precesses. We limit this study to wide-angled fast precession of molecular jets through half-angles of 5°, 10° and 20°. We employ a code that includes molecular hydrogen cooling, dissociation and reformation as well as other cooling functions and chemistry appropriate for the high densities assumed. The jet bores out an annulus of increasing radius but constant width, with strong molecular cooling acting to reduce the drag on the impact region. Nevertheless, the expansion decelerates the outflow advance sufficiently that we predict highly precessing molecular jets can reach 1 pc in size between 30 000 and 100 000 yr. Even on the relatively short (500 yr) time-scale of the simulations, the leading edge of the annulus disrupts into numerous bow shocks and some linear shock structures. Images, position-velocity diagrams and channel maps for H2 and CO transitions are analysed. Testable predictions are made for the upcoming generation of high-resolution submillimetre and far-infrared telescopes. The distributions of both mass and CO emission-line flux with radial velocity are predicted and compared to observations. A clear dependence of the slope of the mass-velocity (or luminosity-velocity) distribution on the precession angle is found, which may help us to interpret the variety of reported line profiles. We compute the evolution of radiative emission relative to the mean jet power for these simulations and previous molecular jet simulations in this series. The H 2 1-0 S(1) emission is roughly a factor of 0.001 of the mean power in the dense jets and 0.01 in the light jets, consistent with the kinetic energy of the light jets being more efficiently radiated.