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

根据流行的星系形成等级理论，当今椭圆星系的聚集历史涉及许多小星系实体的合并。矮不规则星系被广泛认为是大质量星系的可能组成部分。因此，研究矮不规则星系中的古老球状星团（其性质反映了它们早期形成时的物理条件），并与古老椭圆星系中的球状星团进行比较，可以用来量化矮不规则星系对今天大质量星系及其球状星团系统的组成的贡献。博士项目的目标是研究矮不规则星系的球状星团的特性，以阐明组装场景。我们的研究从NGC1427A球状星团系统开始，NGC1427A是天炉座星系团中的一个矮不规则星系。目前，使用深HST/ACS图像研究了大量麦哲伦型球状星团系统，这些不规则星系位于本星系群之外的松散群环境中。颜色（金属丰度）分布、光度函数、特定频率、结构参数和空间分布作为宿主星系光度（质量）的函数，正在被推导出来，以便在分层星系形成场景的背景下讨论结果。这项研究将得到最近获得的更多HST/ACS数据和VLT/VIMOS望远镜的新观测数据的补充。拟议的研究方案是对这种球状星团系统进行调查的一个项目的继续。它是2004年由博士生伊斯克伦·格奥尔基耶夫发起的。在波恩的初始阶段后，Georgiev获得了为期两年（2005-2007）的“STScT奖学金”（研究生研究协会），在那里的科学家的指导下，他在STScI进行研究，与我们在波恩的密切互动和全面监督。这里要求对整个研究计划的最后一年提供支持，以便Georgiev能够在波恩大学的Argelander天文研究所（AlfA）完成他的博士论文。要进行的工作包括完成子项目并公布结果，进一步追求一个更大的子项目以完成，以及准备博士论文及其辩护（博士考试）。

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).