Old Globular Clusters in Dwarf Irregular Galaxies: Probes for the Formation of Massive Galaxies and their Globular Cluster Systems

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According to the popular hierarchies galaxy formation scenario, the assembly history of present-day elliptical galaxies involved numerous mergers of small galactic entities. Dwarf irregular galaxies are widely regarded as being probable building blocks of massive galaxies. Hence, a study of old globular star clusters in dwarf irregular galaxies (whose properties reflect the physical conditions at the time of their early formation) and a comparison with globular star clusters in old elliptical galaxies can be used to quantify the contribution of dwarf irregular galaxies to the assembly of today's massive galaxies and their globular cluster systems. The goal of the PhD project is to investigate the properties of globular clusters of dwarf irregular galaxies to shed light on the assembly scenario.Our investigations have begun with the globular cluster system of NGC1427A, a dwarf irregular galaxy in the Fornax galaxy cluster. Currently, globular cluster systems in a large sample of Magellanic-type, irregular galaxies in loose group environments outside the Local Group is investigated using deep HST/ACS images. Color (metallicity) distributions, luminosity functions, specific frequencies, structural parameters, and spatial distributions as a function of the host galaxy luminosity (mass), are being derived in order to discuss the results in the context of the hierarchical galaxy formation scenario. The study will be complemented with more HST/ACS data that recently became available and new observational data from the VLT/VIMOS telescope.The proposed research programme is a continuation of a project of investigation of such globular cluster systems. It was initiated in 2004 for and with the PhD student Iskren Georgiev. After an initial phase in Bonn, Georgiev won a "STScT Fellowship" (a Graduate Student Research Associateship) of two years (2005-2007), during which he carries out research at the STScI under the guidance of scientists there, with strong interaction with and overall oversight by us in Bonn.Here support for the final year of the entire research programme is requested, so that Georgiev can complete his PhD Thesis at the Argelander Institute for Astronomy (AlfA) of the University of Bonn. The work to be carried out consists of finishing subprojects with publication of the results, pursuing further a larger subproject to be brought to completion as well as the preparation of the PhD Thesis with its defence (PhD exam).