H2 Rotational Transition Emission From Molecular Cloud Edges: Tracing the Energy Input Affecting Cloud Structure and Evolution

Details H2 Rotational Transition Emission From Molecular Cloud Edges: Tracing the Energy Input Affecting Cloud Structure and Evolution H2 Rotational Transition Emission From Molecular Cloud Edges: Tracing the Energy Input Affecting Cloud Structure and Evolution

May 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006sptz.prop30326g&link_type=abstract

Spitzer Proposal ID #30326

Computer Science

Scientific paper

We propose a study of the boundaries of molecular clouds to investigate the role of turbulent energy dissipation in heating these regions. Energy dissipated in cloud boundary layers may be injected into the molecular cloud, helping to support the dense region against gravitational collapse and thus lengthening the time available for star formation. Standard models of cloud boundaries predict only a limited quantity of warm H2, insufficient for detection at the present time. The inclusion of turbulent dissipation, suggested theoretically and by observations of diffuse clouds, can radically change the situation, resulting in > 10^{20} /cm^2 of H2 at temperatures > 100 K., sufficient for detection with Spitzer IRS. The warm H2 is plausibly located outside the region traced by carbon monoxide, thus forming a layer between the atomic hydrogen halo and the cooler molecular gas. We propose to carry out observations of three areas in the Taurus molecular cloud complex, including several boundaries demarcated in a carbon monoxide study of this region. Both the morphology and the kinematics of the 12CO and 13CO data indicate that the cloud edges are highly structured. By observing strips containing 11 pointings spaced over 30' with the LL1, LL2, and SL1 configurations of the IRS, we can observe the 4 lowest rotational transitions of H2 from within the bulk of the cloud, through the boundary, and beyond the cloud limits. We anticipate likely detection of the lowest [S(0); 28 micron] transition of para-H2, plausibly the lowest [S(1); 17 micron] transition of ortho-H2, and possibly the next higher transitions of each species. The critical point is that the relative intensities of the higher-J transitions are very sensitive to temperature, and thus are superb probes of heating above that predicted by "quiescent cloud" models. We thus feel that these Spitzer observations will make a very significant contribution to our understanding of molecular cloud structure and evolution.

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