Probing the Clumpy Nature of Molecular Clouds

Details Probing the Clumpy Nature of Molecular Clouds Probing the Clumpy Nature of Molecular Clouds

Feb 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt........27p&link_type=abstract

PhD Thesis, Department of Astronomy, Seoul National University, Korea, 1997.

Astronomy and Astrophysics

Astronomy

1

Scientific paper

We investigated the excitation conditions and the line formation mechanism of molecular transitions in the clumpy structured clouds and the dense molecular cores. It is generally accepted that the clouds or cores are composed of many small clumps. However, have been done little model studies on the radiative transfer of molecular lines in such clumpy medium. This study is aimed at knowing how the emission lines are formed in the clumpy clouds and how they reflect the kinematics and structure of the clumps. First we developed a three dimensional radiative transfer code by using the Monte Carlo method, and simulated the clumpy structure of the cloud as realistically as possible. It is found that the excitation conditions in the clumpy cloud are more uniform than those of the smoothly varying density structure. The tendency of uniformity is pronounced under the dominance of macroturbulent motion of the clumps. When the space between the clumps is left empty, the CO line profiles calculated in these conditions do not show the time long self-absorption features, and are compatible with the observed line characteristics. An inclusion of very dilute inter-clump matter results in a development of the self-absorption features or the flat tops to the line center. This suggests that a very large density contrast exists between the clump and inter-clump media. The tendency of the uniform excitation conditions is also noted for the CS transitions, if the dense cores are clumpy. We applied our clumpy model to the NGC2071 dense core, for which multi-transitional observations of CS are available. The clumpy model fits the observations much better than the microturbulent one. It was found that the volume fraction occupied by the clumps is only 5% and the mean density gradient is steeper than that estimated by the previous study. The first half of the thesis was already published in A&A, 300, 890 and in A&A, 312, 981.

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