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