H2 excitation imaging of the Orion Molecular Cloud

Abstract

Observations are reported of IR emission in H2, around 2 μm in the K-band, obtained with the ESO 3.6 m telescope using the ADONIS adaptive optics system. Data cover a region of the Orion Molecular Cloud north of the Trapezium stars and SW of the Becklin-Neugebauer object. Excellent seeing yielded diffraction limited images in the v = 2-1 S(1) line at 2.247 μm. Excitation temperature images were created by combining these data with similar data for H2 emission in the v = 1-0 S(1) line reported earlier (Vannier et al. 2001). Shock models are used to estimate densities in emitting clumps of material. In local zones with high excitation temperatures, post-shock densities are found to be as high as several times 108 cm-3, an order of magnitude denser than our previous estimates. We propose that the nature of these zones is dictated by the combined activity of shocks, which create dense structures, and the powerful radiation field of θ1C Ori which photoevaporates the boundaries of these structures.