The internal dynamics of globular clusters and ultra-compact dwarf galaxies


Thesis Supervisor: Michael Hilker




Globular clusters (GCs) are believed to be purely baryonic systems without any dark matter (DM). So far, radial velocity measurements of large samples of stars in Galactic GCs seem to support a Newtonian behaviour of their kinematics without the need of dark matter. However, in the recent years, it has been demonstrated that many, predominantly massive Galactic GCs harbour multiple stellar populations pointing to a complex star and formation and enrichment history. This normally is more typical for dark matter dominated dwarf galaxies. Probably some of the Galactic GCs are remnant nuclei of disrupted satellite galaxies (e.g. omega Cen and M54). So one might expect that some GCs might have retained a certain amount of dark matter.

In the same line of thoughts, the dividing line between star clusters and dwarf galaxies seems to blur with the advent of the so-called ultra-compact dwarf galaxies (UCDs) and ultra-faint dwarf spheroidals. Whereas the latter seem to be DM dominated according to the kinematical analysis of small samples of stars, this has not been shown for UCDs yet. Those are at larger distances and only integral velocity dispersions can be analysed. Only for few of them one can hope to get spatially resolved kinematics.

This PhD project aims at studying observationally as well as theoretically the internal dynamics of globular clusters and ultra-compact dwarf galaxies. Some radial velocity data of large samples of stars in Galactic GCs do exist. Also spatially resolved IFU spectra of UCDs might get available. The theoretical work should focus on the development of appropriate analysis tools that consider effects like 1) orbital anisotropies, 2) internal rotation, 3) binaries, 4) mass segregation, 5) external tidal field, 6) dark matter halo, and 6) intermediate-mass blach holes. A further aim is to explore how all these effects influence the observed integral line-of-sight velocity distribution in barely resolved external GCs and UCDs.

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