The importance of binary systems for stellar population studies of early-type galaxies

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Early-type galaxies are crucial benchmarks for our detailed understanding of the complex star-formation and mass-assembly histories of galaxies in the local Universe. Stellar population synthesis models allowing us to trace these histories are, however, fundamentally limited by their input physics. Particularly, very few (if any) population synthesis models include the potentially important effects of large numbers of binary stars. Here, the associated research groups leaded respectively by Drs. Zhongmu Li (PR. China) and Thorsten Lisker (Germany) propose to expand our state-of-the-art model suite by properly accounting for the observational properties of binary systems and their interactions, leading to a new, state-of-the-art composite single+binary-star population synthesis model, which will be made publicly available. We will then apply this significantly improved model to carefully chosen samples of representative early-type dwarf and giant galaxies, in order to investigate their stellar populations in detail. This will be a major step forward in obtaining robust and conclusive results regarding their star formation and mass assembly histories, and in particular the correlation of these with galaxy mass and environmental density. Our study thus directly aims at significantly improving our understanding of the physical processes governing the formation and evolution of galaxies. The project will be founded on the fruitful cooperation of the Chinese and German research groups. It will finish in 2 years, and we foresee that 3 or more scientific publications will be submitted to internationally renowned peer-review journals. It will give benefit to the astrophysical researches of both China and Germany, and will improve the research communications between Chinese and German scientists in the field of astronomy and astrophysics.