2011A&A...529A..24Z

We present sensitive high angular resolution submillimeter and millimeter observations of torsionally/vibrationally highly excited lines of the CH₃OH, HC₃N, SO₂, and CH₃CN molecules and of the continuum emission at 870 and 1300µm from the Orion KL region, made with the Submillimeter Array (SMA). These observations and SMA CO J=3-2 and J=2-1 imaging of the explosive flow originating in this region suggest that the molecular Orion ``hot core'' is a pre-existing density enhancement heated from the outside by the explosive event. Unlike in other hot cores, we do not find any self-luminous submillimeter, radio, or infrared source embedded in the hot molecular gas, nor observe filamentary CO flow structures or ``fingers'' in the shadow of the hot core pointing away from the explosion center. The low-excitation CH₃CN emission shows the typical molecular heart-shaped structure, traditionally named the hot core, and is centered close to the dynamical origin of the explosion. The highest excitation CH₃CN lines all originate from the northeast lobe of the heart-shaped structure, i.e. from the densest and most highly obscured parts of the extended ridge. The torsionally excited CH₃OH and vibrationally excited HC₃N lines appear to form a shell around the strongest submillimeter continuum source. All of these observations suggest that the southeast and southwest sectors of the explosive flow have impinged on a pre-existing very dense part of the extended ridge, thus creating the bright Orion KL hot core. However, additional theoretical and observational studies are required to test this new heating scenario.