The extinction toward the molecular and atomic line emitting regions is estimated from relative line intensities, and it is found that the H2 emission arises from within the OMC-1 cloud at an average K-band extinction of 1.0 mag, whereas the atomic hydrogen emission and much of the fine structure emission comes from the foreground H II region and its bounding photodissociation front.
The total H2 luminosity in the ISO-SWS aperture is estimated at (17 ± 5) Lsun, and extrapolated to the entire outflow, (120 ± 60) Lsun. The H2 level column density distribution shows no signs of fluorescent excitation or a deviation from an ortho-to-para ratio of three. It shows an excitation temperature which increases from about 600 K for the lowest rotational and vibrational levels to about 3200 K at level energies E(v,J)/k > 14000 K. No single steady state shock model can reproduce the observed H2 excitation. The higher energy H2 levels may be excited either thermally in non-dissociative J-shocks, through non-thermal collisions between fast ions and molecules with H2 in C-shocks, or they are pumped by newly formed H2 molecules. The highest rotational levels may be populated by yet another mechanism, such as the gas phase formation of H2 through H-.
Keywords: Shock waves -- ISM: individual objects: Orion Peak 1 -- ISM: molecules -- Infrared: ISM: lines and bands
Status: A&A accepted
Address:mailto: rosental@mpe.mpg.de
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Last update: 23-Mar-2000 by L.E. Tacconi-Garman