Volume 366, Number 2, February I 2001
|Page(s)||651 - 661|
|Published online||15 February 2001|
H2 infrared emission and the formation of dense structures in the Orion molecular cloud
Observatoire de Paris-Meudon, 92195 Meudon Principal Cedex, France
2 Université de Cergy-Pontoise UMR 8588 du CNRS, 95806 Cergy Cedex, France
3 Institute of Physics and Astronomy, University of Aarhus, 8000 Aarhus C, Denmark and Observatoire de Paris-Meudon, UMR 8588 du CNRS, France
4 Theoretical Astrophysics Centre, University of Aarhus, 8000 Aarhus C, Denmark
Corresponding author: D. Field, email@example.com
Accepted: 9 November 2000
Observations are reported of IR emission of H2 from a region of the Orion molecular cloud (OMC1) between the Becklin-Neugebauer object and IRc2 to the north and the Trapezium stars to the south. Data were obtained using the ESO 3.6 m telescope in the K-band around 2 μm with the ADONIS adaptive optics system. Images of (1) show a spatial resolution of ∼0.15''. Detailed investigations of the distribution of sizes of structures in our images have been performed by area-perimeter analysis, Fourier analysis and brightness distribution studies. These demonstrate that structure is not fractal but shows a preferred scales of between 3 10-3 and 4 10-3 pc. In an attempt to estimate the density in observed structures, predictions of both shock models and photodissociation region models have been compared with measured emission brightness in the (1) line. Magnetic (C-type) shocks with velocities of 30 km s-1 and pre-shock densities of 106 cm-3 yield the best representation of our data, notwithstanding significant discrepancies for the brightness ratio between (1) and (1) lines. Our results show that post-shock densities are several times 107 cm-3. This is sufficiently high that the passage of C-type shocks in Orion yields gravitational instability which may in turn trigger star formation in the post-shock gas.
Key words: ISM: individual objects: OMC1 / ISM: kinematics and dynamics / ISM: molecules / shock waves / infrared: ISM: lines and bands
© ESO, 2001
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