Anatomy of the Photodissociation Region in the Orion Bar
A. G. G. M. Tielens 1,
M. M. Meixner 2,
P. P. van der Werf 3,
J. Bregman 1,
J. A. Tauber 4,
J. Stutzki 5, and
D. Rank 6
1 MS 245-3 NASA Ames Research Center, Moffett Field, CA 94035-1000
2 Radioastronomy Laboratory, University of California, Berkeley, CA 94720
3 Max Planck Institut für Extraterrestrische Physik, Giessenbach Strasse, D-8046 Garching bei München, Germany
4 Radioastronomy Laboratory, University of California, Berkeley, CA 94720, and ESAAstrophysics Division, ESTEC, P.O. Box 299, NL-2200 AG Noordwijk, the Netherlands
5 I. Physikalisches Institut, Universitat Köln, Zülpicherstrasse 77, W-5000 Köln 41, Germany
6 Lick Observatories, University of California, Santa Cruz, CA 95060
Much of the interstellar gas resides in photodissociation regions whose chemistry and energy balance is controlled by the flux of far-ultraviolet radiation upon them. These photons can ionize and dissociate molecules and heat the gas through the photoelectric effect working on dust grains. These regions have been extensively modeled theoretically, but detailed observational studies are few. Mapping of the prominent Orion Bar photodissociation region at wavelengths corresponding to the carbon-hydrogen stretching mode of polycyclic aromatic hydrocarbons, the 1-0 S(1) line of molecular hydrogen, and the J = 1-0 rotational line of carbon monoxide allows the penetration of the far-ultraviolet radiation into the cloud to be traced. The results strongly support the theoretical models and show conclusively that the incident far-ultraviolet radiation field, not shocks as has sometimes been proposed, is responsible for the emission in the Orion Bar.
Submitted on June 7, 1993
Accepted on August 2, 1993
