Astron. Astrophys. 327, 309-316 (1997)

17 µm molecular hydrogen line emission from OMC-1

Michael G. Burton ¹ and Michael R. Haas <sup>2

1</sup> School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
² Space Science Division, NASA/Ames Research Center, MS245-6, Moffett Field, California 94035-1000, USA

Received 17 March 1997 / Accepted 27 May 1997

Abstract

The v=0-0 S(1) line of molecular hydrogen at 17.03 m has been measured in the source OMC-1 along a cut passing through the near-IR H₂ emission Peaks 1 and 2 using the Kuiper Airborne Observatory. The line flux is typically 50% of the 2.12 m v=1-0 S(1) line, but its distribution is somewhat more extended and it is relatively brighter at Peak 2. We interpret this as shocked emission coming from two regions of roughly equal brightness and lying close to the plane of the sky, plus a more extended contribution from slower shocks ( ) which do not contribute significantly to the near-IR vibrational-rotational lines. The 17 m line flux is an order of magnitude too strong to be explained by planar J- and C-shock models. However our data cannot distinguish between the merits of a cooling flow dominated by H₂ line emission and the integrated emission from a C-type bow-shock. Both models predict column density ratios close to those observed from a variety of lines covering a range from 1 000 to 25 000 K in upper state energy. We predict a flux for the ground state 28.2 m 0-0 S(0) line of that of the 1-0 S(1) line at Peak 1, and suggest that a consistent set of observations of the lowest pure rotational lines of H₂ would allow us to distinguish between these shock models.

Key words: ISM: molecules - ISM: individual objects (OMC-1) - shock waves - molecular processes - techniques: spectroscopic - infrared: ISM: lines and bands

Send offprint requests to: M.G. Burton

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Contents

• 1. Introduction
• 2. Observations
• 3. Results
• 4. Discussion
  • 4.1. Column Density Ratios (CDR )
  • 4.2. Comparison to shock models
    • 4.2.1. Cooling flows
    • 4.2.2. Bow shocks
    • 4.2.3. Cooling function for low temperatures
  • 4.3. Predictions for pure rotational lines
• 5. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: April 8, 1998
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