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

Abstract

Most simulations of outflow feedback on star formation are based on the assumption that outflows are driven by a wide angle "Xwind," 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 and grid refinement down to 5 au, on timescales up to 10 000 yrs. Then we computed the predicted properties for the purposes of a comparison with observational data. First, the jet-driven shell expands much 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 shows 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, with a sheared velocity field along the shell walls and a base opening angle reaching up to α 90 • . Third, at realistic ages of ∼10 000 yrs, a pulsed jet-driven shell shows fitting features along with a qualitative resemblance with recent observations of protostellar outflows with the Atacama Large Millimeter Array, such as HH46-47 and CARMA-7. In particular, similarities can be 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, taking into account a realistic ambient density stratification in addition to millenia-long integration times is equally essential to reliably predict the properties of outflows driven by a pulsed jet and to confront them with the observations.

The Evolution of Protostellar Outflow Cavities, Kinematics, and Angular Distribution of Momentum and Energy in Orion A: Evidence for Dynamical Cores

“…One possible interpretation is that (non-precessing) jet-like prostellar winds can produce a much wider molecular outflow, even if the original wind has a very narrow momentum angular distribution and without the aid of another (much wider) wind component. This could be produced, for example, by the sideways ejection of material by a series of internal working surfaces (Raga et al 1993), turbulent mixing of the jet and a turbulent envelope (Offner & Chaban 2017), or the expanding shell driven by a pulsed jet in a stratified core (Rabenanahary et al 2022).…”

Shedding Light on the Ejection History of Molecular Outflows: Multiple Velocity Modes and Precession

“…Two recent works use PV diagrams to compare their simulations with observations of molecular outflows. Rabenanahary et al (2022) compared simulations of an outflow driven by a pulsed jet and observations in CARMA-7 by Plunkett et al (2015). Rivera-Ortiz et al (2023) carried out simulations of a jet aimed at reproducing the Cepheus E outflow observed by de Schutzer et al (2022).…”

JWST Peers into the Class I Protostar TMC1A: Atomic Jet and Spatially Resolved Dissociative Shock Region

“…Protostellar outflows are often described as consisting of a collimated jet and a slower wide-angle wind, even though distinctions between the components and their physical origins are debated (Arce et al 2007). The jet component denotes the fast and collimated outflow that is likely responsible for entrainment on scales >5000 au as observed through, e.g., CO emission (Rabenanahary et al 2020;de A. Schutzer et al 2022). Meanwhile, a slower wide-angle disk wind points to the small-scale (<500 au) outflow which is closely related to the protoplanetary disk.…”