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    The L1495-B218 Filaments in Taurus Seen in NH₃ & CCS and Dynamical Stability of Filaments and Dense Cores

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    Author
    Seo, Youngmin
    Issue Date
    2016
    Keywords
    Clouds
    ISM
    Molecules
    Radio Lines
    ISM
    Stars
    Formation
    Astronomy
    ISM
    Advisor
    Shirley, Yancy L.
    
    Metadata
    Show full item record
    Publisher
    The University of Arizona.
    Rights
    Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
    Abstract
    We present deep NH₃ and CCS maps of L1495-B218 filaments and the dense cores embedded within the filaments in Taurus. The L1495-B218 filaments form an interconnected, nearby, large complex extending over 8 pc. We observed the filaments in NH₃ (1,1)&(2,2), CCS Nⱼ = 1₂-0₁, and HC₇N J = 21-20 with spectral resolution of 0.038 km/s and spatial resolution of 31". The CSAR algorithm, which is a hybrid of seeded-watershed and binary dendrogram algorithm, identifies 39 leaves and 16 branches in NH₃ (1,1). Applying a virial analysis for the 39 NH₃ leaves, we find only 9 out of 39 leaves are gravitationally bound, and 12 out of 30 gravitationally unbound leaves are pressure-confined. Our analysis suggests that a dense core may form as a pressure-confined structure, evolve to a gravitationally bound core, and then undergo collapse to form a protostar. We find that the L1495A, B213E, and B216 regions have strong CCS emission and the B211 and B218 regions have weak CCS emission. Analysis of CCS emission with NH₃ (1,1) and dust continuum emission shows that CCS is not a good tracer for starless core evolution. On the other hand, CCS appears to trace recently accreted gas in L1495A and L1521D. We also present more realistic dynamic stability conditions for dense cores and filaments. In a new analysis of stability conditions we account for converging motions which have been modeled toward starless cores and take the effect of radiation fields. We find that the critical size of a dense core having a homologous converging motion with its peak speed being the sound speed is roughly half of the critical size of the Bonnor-Ebert sphere. We also find the critical mass/line density of a dense core/filament irradiated by radiation to be considerably smaller than that of the Bonnor-Ebert sphere/isothermal cylinder when the radiation pressure is stronger than the central gas pressure of dense core/isothermal cylinder. For regions in the inner Galaxy and near OB associations, the critical mass/line density of a dense structure may be less than 20% of the critical mass/line density of Bonnor-Ebert sphere/isothermal cylinder.
    Type
    text
    Electronic Dissertation
    Degree Name
    Ph.D.
    Degree Level
    doctoral
    Degree Program
    Graduate College
    Astronomy
    Degree Grantor
    University of Arizona
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