Star formation in molecular clouds




Vutisalchavakul, Nalin

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There has been many recent observations in the area of star formation. High-resolution observations of other galaxies enabled a study of extragalactic star formation in more detailed while large scale surveys of the Milky Way enabled a more comprehensive study of Galactic star formation. The main goal of this thesis is to use multi-wavelength, large-scale observations of the Milky Way to connect Galactic to extragalactic star formation and to study star formation regulation in molecular clouds. We tested the use of extragalactic star formation rate tracers on nearby molecular clouds and found that the total infrared and 24 μm luminosity underestimate star formation rates of nearby molecular clouds by a large factor, indicating a problem of using extragalactic tracers of star formation on small regions and regions with low mass or low star formation rates. We studied the relation between star formation and molecular gas distribution in a 11 square degree of the Galactic Plane on various spatial scales starting from a clump scale of around few parsecs to a scale of ≈ 200 parsec. The result shows a good correlation between molecular gas and star formation on a scale above ≈ 5 − 8′. The star formation relation that is seen on disk-averaged scales in other galaxies shows a large scatter on the small scales. We built a catalog of Galactic molecular clouds with measured star formation rates and studied the relations between properties of molecular clouds and star formation. We tested several models of star formation on the catalog of molecular clouds. We found that the dense gas mass shows significant correlations with star formation rates but the depletion time of dense gas varies with other properties of the clouds. We found that the free- fall efficiency is higher in dense gas compared to the general molecular gas of the clouds.




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