UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Connecting Molecular Clouds to Clustered Star Formation using Interferometry(2018) Dhabal, Arnab; Mundy, Lee G.; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Stars are commonly formed in clusters in dense regions of interstellar medium called molecular clouds. In this thesis, we improve our understanding of the physics of star formation through multiple experiments involving interferometry. We use CARMA observations of filaments in Serpens and Perseus molecular clouds to study their morphology and kinematics using dense gas tracers. The observations are compared against predictions from simulations to explain how filaments form and evolve to form stars. Ammonia inversion transitions data is obtained from VLA observations of the NGC 1333 molecular cloud. From this data, we derive temperature, structural and kinematic information about the gas participating in star formation on scales from 2 parsec to 0.01 parsec, thereby connecting the large scale gas and dust structure to individual protostellar envelopes. These observations from ground-based arrays are complemented by the development of the Balloon Experimental Twin Telescope for Infra-red Interferometry (BETTII). This pioneering instrument performs Michelson interferometry along with Fourier Transform Spectroscopy, thereby providing sub-arcsecond angular resolution and spectroscopic capabilities at far-infrared wavelengths 30-100 microns. Using this capability, BETTII will study the dusty envelopes around protostars in clustered star forming regions. The instrument development is a component of the thesis with focus on the optics designing, evaluation and alignment for the completed and upcoming flights. We discuss how the optical system mitigates the challenges of phase control for such a balloon borne interferometer. Further, interferometric simulations of BETTII observations are carried out to investigate how well these observations can constrain the defining parameters of protostars.Item High-Resolution Imaging of Dense Gas Structure and Kinematics in Nearby Molecular Clouds with the CARMA Large Area Star Formation Survey(2015) Storm, Shaye; Mundy, Lee G; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis utilizes new observations of dense gas in molecular clouds to develop an empirical framework for how clouds form structures which evolve into young cores and stars. Previous observations show the general turbulent and hierarchical nature of clouds. However, current understanding of the star formation pathway is limited by existing data that do not combine angular resolution needed to resolve individual cores with area coverage required to capture entire star-forming regions and with tracers that can resolve gas motions. The original contributions of this thesis to astrophysical research are the creation and analysis of the largest-area high-angular-resolution maps of dense gas in molecular clouds to-date, and the development of a non-binary dendrogram algorithm to quantify the hierarchical nature and three-dimensional morphology of cloud structure. I first describe the CARMA Large Area Star Formation Survey, which provides spectrally imaged \NtwoH{}, \HCO{}, and HCN ($J=1\rightarrow0$) emission across diverse regions of the Perseus and Serpens Molecular Clouds. I then present a detailed analysis of the Barnard~1 and L1451 regions in Perseus. A non-binary dendrogram analysis of Barnard~1 \NtwoH{} emission and all L1451 emission shows that the most hierarchically complex gas corresponds with sub-regions actively forming young stars. I estimate the typical depth of molecular emission in each region using the spatial and kinematic properties of dendrogram-identified structures. Barnard~1 appears to be a sheet-like region at the largest scales with filamentary substructure, while the L1451 region is composed of more spatially distinct ellipsoidal structures. I then do a uniform comparison of the hierarchical structure and young stellar content of all five regions. The more evolved regions with the most young stellar objects (YSOs) and strongest emission have formed the most hierarchical levels. However, all regions show similar mean branching properties at each level, suggesting that dense gas fragmentation proceeds in a hierarchically similar way from earlier to later stages of star formation. Compared to the more evolved YSOs, the youngest YSOs are preferentially forming within leaves and at high-level locations in dendrogram hierarchies, indicating that dense gas in molecular clouds must reach a state of hierarchical complexity before young stars form efficiently.