Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010phdt........23v&link_type=abstract
PhD Thesis, University of Heidelberg, 2010
Physics
Clouds, Molecules, Radio Lines, Star Formation
Scientific paper
The goal of this thesis work is to investigate the initial conditions and the early phases of the formation of high-mass stars by means of dedicated observational studies. We consider two object classes: infrared dark clouds (IRDCs), and a subsequent stage characterized by the presence of young embedded (proto-)stellar clusters. First, we estimate masses and column densities for a completely new sample of southern IRDCs, utilizing our own millimeter continuum emission maps as well as Spitzer satellite data. The parameters we derive show that IRDCs from our sample have the potential to form not only low- and intermediate-mass stars, but can also be the birth places of massive stars. In particular, the comparison of our results with previously obtained data for low-mass starless cores shows a clear trend for IRDCs to have systematically higher column densities. The interpolated IRDC peak column densities exceed the threshold for the onset of massive star formation previously advocated by theoretical studies. We also critically evaluate the limitations of the applied emission and extinction methods. Second, we investigate the physical conditions and the chemical composition of the dense gas within the IRDCs of our sample by means of a multi-line molecular spectroscopy analysis. All the clouds have complex HCO+ line pro les, and we detect SiO emission in some clouds. These ndings mark the presence of infall and out ow motions in at least some parts of the IRDCs, and hence, ongoing star formation. In comparison with low-mass starless cores, the IRDCs have broader and more intense lines. Thus, they may be characterised by more turbulent conditions. Nevertheless, we nd a tendency for the IRDCs to have molecular abundances similar to the case of low-mass starless cores. This indicates similar chemical initial conditions for low- and high-mass star-forming regions. Finally, we study the stellar composition and environmental conditions in the young embedded cluster IRAS 06058+2138. We perform an analysis of all the available data, covering the near- and mid-infrared as well as the centimeter and millimeter wavelength range. In particular new VLT/SINFONI integral- field spectroscopy data have played a pivotal role. We identify three star-forming clusters at different evolutionary stages. Comparing the relative ages of these clusters and their relative locations, we conclude that triggering could not have led to the cluster con guration we see in the region. Thus, we assume a merely sequential star-formation scenario for this region. With this study, we also demonstrate the importance of a multi-wavelength approach. Combining data at different wavelengths allows us to investigate both the more evolved stellar population, as well as very young embedded objects, and hence, to reconstruct the star-forming history of structured cluster environments.
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