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Mora, Marcelo D. (2008): Star clusters in unperturbed spiral galaxies. Dissertation, LMU München: Fakultät für Physik



Stars do not form in isolation, they form in groups known as star clusters. Star clusters are seen in a wide range of galaxies and environments. Their presence reveals the history of the host galaxy and the processes of its star formation. During the last years star clusters have been deeply investigated in violent environments, while the properties of star clusters in more quiet environments have received less attention. Among all unperturbed environments we focus on 5 spiral galaxies with no signs of external perturbations: NGC 45, NGC 1313, NGC 4395, NGC 5236 and NGC 7793. Star clusters lying in these galaxies were observed through HST imaging and VLT spectroscopy. The analysis of star cluster masses, ages, sizes, and their positions on the galaxies, showed that star cluster formation is an ongoing process that depends on the local conditions. The observed star cluster luminosity functions show values consistent with the expected alpha~-2. We found an important number of globular clusters in NGC 45. Their properties are analyzed through photometry and spectroscopy. Photometry suggests that these globular clusters belong to a single metal poor population. Spectroscopy confirmed this for the 8 brightest ones. Velocities indicate halo or bulge kinematics. Absorption spectrum features indicate ages of the order of Gyr and [alpha/Fe] values lower than the Milky Way globular clusters, but similar to dwarf galaxies in the local group.