The Orion fingers: Near-IR adaptive optics imaging of an explosive protostellar outflow

Aims: Adaptive optics (AO) images are used to test the hypothesis that the explosive BN/KL outflow from the Orion OMC1 cloud core was powered by the dynamical decay of a non-hierarchical system of massive stars.
Methods: Narrow-band H₂, [Fe ii], and broad-band K_s obtained with the Gemini South multi-conjugate AO system GeMS and near-IR imager GSAOI are presented. The images reach resolutions of 0.08 to 0.10'', close to the 0.07'' diffraction limit of the 8-m telescope at 2.12 μm. Comparison with previous AO-assisted observations of sub-fields and other ground-based observations enable measurements of proper motions and the investigation of morphological changes in H₂ and [Fe ii] features with unprecedented precision. The images are compared with numerical simulations of compact, high-density clumps moving ~10³ times their own diameter through a lower density medium at Mach 10³.
Results: Several sub-arcsecond H₂ features and many [Fe ii] "fingertips" on the projected outskirts of the flow show proper motions of ~300 km s^-1. High-velocity, sub-arcsecond H₂ knots ("bullets") are seen as far as 140'' from their suspected ejection site. If these knots propagated through the dense Orion A cloud, their survival sets a lower bound on their densities of order 10⁷ cm^-3, consistent with an origin within a few au of a massive star and accelerated by a final multi-body dynamic encounter that ejected the BN object and radio source I from OMC1 about 500 yr ago.
Conclusions: Over 120 high-velocity bow-shocks propagating in nearly all directions from the OMC1 cloud core provide evidence for an explosive origin for the BN/KL outflow triggered by the dynamic decay of a non-hierarchical system of massive stars. Such events may be linked to the origin of runaway, massive stars.

The final set of FITS files is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/579/A130