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Galaxy Evolutionary Synthesis Models
help you understand your data on star clusters and galaxies from the early universe until today in terms of their relevant physical and chemical properties and their evolutionary state.

Star Formation, Chemical Enrichment and Mass Assembly Histories of Galaxies:
The Astro-Archaeological Approach

In the Astro-Archaeological approach we use star clusters, their ages and chemical abundances in local galaxies of various types/masses as fossil records of their parent galaxy SFH, CEH and MAH.   

The Astro-Archaeological is an entirely new one. Its power has only recently been realised, partly thanks to our involvement. It has become clear that 
1. star cluster formation is a major mode of all active star formation and the dominant mode in the strongest starbursts, i.e. those accompanying mergers of gas-rich spirals where, together with short-lived, low-mass clusters significant populations of long-lived, high-mass clusters are formed from gas pre-enriched in their parent galaxies, and that
2. since star clusters can be analysed one-by-one, after careful background subtraction, the age distribution of a population of clusters and their chemical abundances yield direct information about the (violent) star formation and chemical enrichment history, over cosmological time scales, of their parent galaxy.

Major mergers increase the mass of a galaxy by about a factor of 2. If the merging galaxies are gas-rich, strong starbursts will be triggered. Mergers and starbursts significantly determine the mass assembly histories of galaxies. Major mergers involving gas-rich galaxies produce rich populations of new star clusters, part of them massive and long-lived. Hence, they leave imprints on the age and metallicity distributions of the star cluster populations that give clues as to the galaxy mass assembly histories of their parent galaxies. How the number of massive and long-lived clusters depends on the properties of the merger/accretion event is investigated in our studies of interacting galaxies, SF and star cluster formation.

In the astroarchaeological approach we analyse multi-band photometric and spectroscopic data on star clusters, available through our collaborations, from an ASTROVIRTEL project, own observations, and from public archives. We use the GALEV evolutionary synthesis code, adapted to the study of star clusters, to derive with high accuracy the age and metallicity distributions of populations of star clusters. From these, in turn, the star formation, chemical enrichment, and mass assembly histories of their parent galaxy, or in the case of mergers, parent galaxies, will be reconstructed all the way from the very onset of star formation in the early universe to the present. With star clusters, this can be done to a much higher precision and further back into the past than from studies - either photometric or spectroscopic - of the galaxy's integrated light, the latter always being dominated by the last major star formation episode. 

With own deep NTT K-imaging of the Globular Cluster (GC) system in VCC 1692 in addition to B and I from the ACS Virgo Cluster Survey, we have recently shown that the red peak of the GC optical colour distribution in this galaxy in fact consists of more than one population with the youngest one only ~1 Gyr old (Kotulla & Fritze (2008).

- Kotulla & Fritze 2008, MNRAS XXX
© 2009 Ralf Kotulla for the GALEV team  -  send comments to webmaster(o)