Other
Scientific paper
May 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005phdt.........2r&link_type=abstract
Thesis (PhD). University of California, Berkeley, 245 pages
Other
Scientific paper
This dissertation presents new observations and analysis methods that provide a fresh perspective on extragalactic giant molecular clouds (GMCs). Using observations of GMCs in several galaxies, this work studies molecular clouds in the context of their host galaxies, searching for variations in cloud populations and their star forming properties. The observations were conducted using the BIMA millimeter interferometer, obtaining high resolution imaging of molecular gas in the galaxies M33, M31 and M64. In the disks of galaxies in the Local Group, GMCs follow the same power-law relationships among their macroscopic properties: mass, radius and line width. However, there are significant differences in the mass distributions of these clouds, suggestive of systematic variations in the GMC formation mechanism in different galaxies. Where the ISM is predominantly atomic, GMCs are invariably found on filaments of HI, but such filaments do not necessarily imply the presence of GMCs. The angular momentum of GMCs in M33 is an order of magnitude lower than expected based on simple formation models from instabilities. The correlation with atomic gas and the low angular momentum suggest that the clouds form out of atomic gas with significant braking in the formation process. In M33 and M31, ~2/3 of the GMCs are correlated with Hα emission, implying a prompt onset of massive star formation. The correlation between GMCs and other objects with known ages or timescales implies that the lifetime of GMCs is 10-30 Myr. This work also presents high resolution observations of GMCs in the molecule rich galaxy M64. The highest mass GMCs in M64 (MGMC>107 Msun) are significantly smaller and denser than expected from extrapolations from lower mass clouds in the Local Group. Such high mass clouds may be responsible for the formation of massive star clusters in starburst systems and their high masses and densities may be necessary to form massive star clusters.
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