H 2 excitation imaging of the Orion Molecular Cloud

Observations are reported of IR emission in H 2, around 2 (mu)m 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 (mu)m. Excitation temperature images were created by combining these data with similar data for H 2 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 10 ^8 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 (theta)^1C Ori which photoevaporates the boundaries of these structures.