Numerical simulations of protostellar jets with nonequilibrium cooling. III. three-dimensional results

In the third of three papers, we present three-dimensional time-dependent numerical simulations of the propagation of protostellar jets into uniform and plane-stratified ambient media using a nonequilibrium treatment of optically thin radiative cooling. We find the evolution of the jet beam and cocoon is similar to the results of previous two-dimensional simulations, including the formation of a thin dense shell at the head of the jet. However, in three dimensions this shell undergoes significant nonaxisymmetric fragmentation to form discrete knots and filaments. Knots shed from the head of the jet propagate nearly ballistically into the ambient gas and can be characterized as "interstellar bullets." On the other hand, variations in the speed of advance of the Mach disk can cause knots formed in the cooling shell to become embedded in the jet beam, leading to "shocked cloudlets." When the jet propagates through an ambient medium with a lateral density gradient, the bow shock propagates more slowly in the direction of the highest densities as expected, leading to a distorted cocoon. However, we find the orientation of the bow shock at the tip of the jet is time variable as the dense shell fragments. Synthetic Hα emission maps and position-velocity diagrams are presented for direct comparison to observations.