2000/02/24 by Dirk Rosenthal, Rosenthal, Dirk, Frank Bertoldi +5
Earth and Planetary Sciences · Physics and Astronomy · #Astrophysics (astro-ph) #FOS: Physical sciences #Geophysics and Gravity Measurements #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/0002456
22 pages, 12 figures, A&A accepted
arxiv created 2000/02/24 · openalex publication_date 2000/02/24 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Using the Short-Wavelength-Spectrometer on the Infrared Space Observatory (ISO), we obtained near- and mid-infrared spectra toward the brightest H2 emission peak of the Orion OMC-1 outflow. A wealth of emission and absorption features were detected, dominated by 56 H2 ro-vibrational and pure rotational lines reaching from H2 0-0 S(1) to 0-0 S(25). The spectra also show a number of H I recombination lines, atomic and ionic fine structure lines, and molecular lines of CO and H2O. Between 6 and 12 mu the emission is dominated by PAH features. 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 > 14 000 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-.