The Effects of Molecular Cloud Structure on its CO Emission and Star Formation

Abstract

In this thesis, we examine how cloud structure affects 3 aspects of star formation studies~--- (1)~The distribution of protostars in molecular clouds. (2) The star formation rate and efficiency. (3) Carbon monoxide observations of molecular clouds. We investigate how star formation and our observations of molecular clouds are related to the density structure of those clouds. In the first chapter we investigate if protostars can form away from the extended high density gas in molecular clouds through SED fitting of protostars found in the low density gas of the Orion Molecular cloud. We find that most of the objects had been misclassified and that those which are young can be associated with and likely originate in the extended high density gas, demonstrating a fairly marked threshold to star formation in the Orion Molecular Cloud. In the second chapter we look at the connection between cloud structure and the star formation rate in the California Molecular Cloud, finding that a lack of high density gas limits star formation at the highest densities and that at low density, the large area, containing few to no protostars, creates a practical star formation threshold. In the third and final chapter we investigate variations in the relationship between carbon monoxide (CO) and dust in the California Molecular Cloud. We observe CO freeze out of the gas phase onto dust grains in the inner portions of clouds, with the depth that occurs at being sensitive to the local dust temperature or star formation. We make the first maps of CO depletion on GMC scales and use depletion as a novel way to identify cores which are undergoing, or likely will undergo, star formation. In summary, while this thesis is embedded among a great deal of ongoing work in the astronomy community, it takes important steps forward in solidifying our understanding of the importance of cloud structure on star formation and our ability to accurately observe GMCs.