Wide-angle protostellar outflows driven by narrow jets in stratified cores

TL;DR

This study demonstrates that pulsed narrow jets in stratified cores can produce wide-angle outflows with properties similar to observations, challenging the necessity of wide-angle wind models in star formation feedback.

Contribution

It shows that narrow, pulsed jets in density-stratified cores can replicate observed outflow features, questioning the traditional reliance on wide-angle wind assumptions.

Findings

Jet-driven shells expand faster in stratified cores.

Shell widths and opening angles resemble observed outflows.

Simulated outflows match ALMA observations in morphology and kinematics.

Abstract

Most simulations of outflow feedback on star formation are based on the assumption that outflows are driven by a wide angle "X-wind," rather than a narrow jet. However, the arguments initially raised against pure jet-driven flows were based on steady ejection in a uniform medium, a notion that is no longer supported based on recent observations. We aim to determine whether a pulsed narrow jet launched in a density-stratified, self-gravitating core could reproduce typical molecular outflow properties, without the help of a wide-angle wind component. We performed axisymmetric hydrodynamic simulations using the MPI-AMRVAC code with optically thin radiative cooling on timescales up to 10000 yrs. Then we computed and compared the predicted properties with observational data. First, the jet-driven shell expands faster and wider through a core with steeply decreasing density than through an uniform core. Second, when blown into the same singular flattened core, a jet-driven shell has a similar width as a wide-angle wind-driven shell in the first few hundred years, but a decelerating expansion on long timescales. The flow adopts a conical shape and a base opening angle reaching up to $90\unicode{xb0}$. Third, after $\sim$ 10000 yrs, a pulsed jet-driven shell shows fitting features and a qualitative resemblance with recent observations of protostellar outflows with the Atacama Large Millimeter Array (ALMA), such as HH46-47 and CARMA-7. In particular, similarities are seen in the shell widths, opening angles, position-velocity diagrams, and mass-velocity distribution, with some showing a closer resemblance than in simulations based on a wide-angle "X-wind" model. Therefore, a realistic ambient density stratification in addition to millenia-long integration times are equally essential to reliably predict the properties of outflows driven by a pulsed jet and to confront them with the observations.