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Gullberg, Bitten (2016): Exploring star formation in high-z galaxies using atomic and molecular emission lines. Dissertation, LMU München: Fakultät für Physik



The conditions under which stars are formed and the reasons for triggering and quenching of starburst events in high-z galaxies, are still not well understood. Studying the interstellar medium (ISM) and the morphology of high-z galaxies are therefore key points in order to understand galaxy evolution. The cosmic star formation rate density peaks between 1<z<3. This period in the history of the Universe is therefore crucial to investigate in order to know more about the star-formation triggering and quenching mechanisms. Phenomena such as major mergers and galactic nuclear activity are believed to be mechanisms dominating the star formation activity at this period of time. It is therefore necessary to study galaxy populations which show signs of major merger events and active galactic nuclei (AGN). This thesis presents three studies of the ISM in high-z galaxies and their morphologies by: Exploring the physical conditions of the ISM in a sample of dusty star-forming galaxies (DSFGs) using the relative observed line strength of ionised carbon ([CII]) and carbon monoxide (CO). We find that the line ratios can best be described by a medium of [CII] and CO emitting gas with a higher [CII] than CO excitation temperature, high CO optical depth tau(CO)>>1, and low to moderate [CII] optical depth tau(CII)<1. Combining millimetre/sub-millimetre and optical data cubes for the high-z radio galaxy (HzRG) MRC0943-242, has revealed a much more complicated morphology than seen in the individual data sets. The millimetre/sub-millimetre observations data have allowed us to spatially separate of the AGN and starburst dominated components, which ~65 kpc apart. The optical data reveal structures of emitting and absorbing gas at multiple wavelengths. A deep high resolution millimetre/sub-millimetre study of the HzRG MRC1138-262, shows emission from water (\water) and an unusually large amount of neutral atomic carbon ([CI]) relative to highly excited CO compared to lensed DSFGs. The detection of water (H2O) emission, which is not associated with the 246GHz continuum emission, suggests excitation by shocks.The uncommon line ratio between [CI]2-1 and CO(7-6) might be due special conditions of the ISM in MRC1138-262 dominated by cosmic rays or differential lensing in other DSFGs thereby not representing the intrinsic ratio. These three studies of the physical conditions of the ISM and morphology of high-z galaxies at z>2, pave the road for future investigations of the star-forming ISM in high-z galaxies, by illustrating the importance of multi-wavelength, fine structure- and molecular line studies.