Formation and evolution of star clusters in interacting galaxies

Details Formation and evolution of star clusters in interacting galaxies Formation and evolution of star clusters in interacting galaxies

Feb 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006phdt........20a&link_type=abstract

PhD thesis, Georg-August-Universität Göttingen, Germany

Astronomy and Astrophysics

Astronomy

Star Cluster, Interacting Galaxies, Active Star Formation, Photometry, Parameter Determination

Scientific paper

My present PhD thesis "Formation and evolution of star clusters in interacting galaxies" and the associated work was performed in the Galaxy Evolution Group at the Institut für Astrophysik (Georg-August-Universität Göttingen, Germany) under supervision of apl. Prof. Dr. U. Fritze - v. Alvensleben. My co-supervisor - especially for the observational part of the thesis - was Dr. R. de Grijs (Department of Physics & Astronomy, University of Sheffield, UK).
In the course of my PhD project I got involved in a number of projects, spanning a wide range of astrophysical topics. The results of these projects are reported in my PhD thesis:
* evolutionary synthesis modeling: I played a leading role in the most recent updates of the GALEV code (originally built by U. Fritze - v. Alvensleben). I have implemented gaseous emission effects to the code (see Anders & Fritze - v. Alvensleben 2003). Only due to this update, models for younger ages than before became possible, allowing for more direct and detailed studies of star and star cluster formation processes. In addition, I have implemented a variety of new filter systems (models in a comprehensive set of regularly used filter sets, including all relevant filters on-board the HST, are now available) eliminating the need to transform between different filter systems and avoiding the associated uncertainties.
* cluster parameter determination: I have developed and thoroughly tested the AnalySED tool (Anders et al. 2004b). This tool allows for statistically robust parameter determination from multi-wavelength broad-band observations of (initially) star clusters. The AnalySED tool has been successfully applied to a large number of star cluster systems (e.g. Anders et al. 2004a; de Grijs et al. (incl. Anders) 2003a,b,c, 2004; de Grijs & Anders 2006, MNRAS, in press)
* uncertainties inherent to evolutionary synthesis modeling and parameter determination: I reported very detailed on a large number of tests on the accuracy of the AnalySED tool, the most detailed study of its kind so far (Anders et al. 2004b). In further work we could establish, again for the first time, the relative accuracy between different working groups using the same dataset, but different models/methods (de Grijs, Anders et al. 2005) and the relative accuracy between parameter determination from broad-band imaging and from CMD fitting (de Grijs & Anders 2006, MNRAS, in press).
* image reduction, source selection, size determination and photometry of clusters from HST imaging:
1. I have studied the young star cluster system in the nearby dwarf starburst galaxy NGC 1569 (Anders et al. 2004a). The most interesting result we found is a change of the cluster mass function during the starburst, in a sense that there is a higher fraction of high-mass clusters formed in the beginning of the burst than in recent times (i.e. the end of the starburst).
2. I am studying the young star cluster system in the nearest major galaxy merger pair, the Antennae galaxies. We performed careful and reproducible cluster selection and completeness determination, and built an advanced statistical tool in collaboration with 2 statisticians to test the cluster luminosity function on the existence of a turnover. We find that a turnover is preferred at a 99.9% level compared to a power-law luminosity function, contradicting previous results not only for the Antennae young star cluster system. We believe that this originates from the careful completeness determination and the advanced statistical methods involved.
3. From the theoretical point-of-view I studied methods to improve the size determination and aperture photometry of extended sources (e.g. nearby star clusters, which are clearly extended though not resolved into single stars in high-resolution imaging). In Anders, Gieles & de Grijs (2006, A&A, in press) we provide a "cookbook" for accurate size determination and aperture corrections for such extended objects.
* cluster disruption in evolutionary synthesis modeling: Dynamical models of star cluster evolution show clear signs of mass segregation (in a sense that high-mass stars sink towards the cluster center, and low-mass stars are transfered to the cluster outskirts). The low-mass stars in the cluster outskirts get easiest stripped off by interaction with the gravitational potential of their host galaxy. This changes the stellar mass function within the cluster, therefore changes its spectrophotometry, resulting in changes of the determined cluster ages when compared to standard evolutionary synthesis models. These age changes can amount up to a factor of ten (Lamers, Anders & de Grijs, in press).

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