A spectroscopic census of galaglic globular clusters with MUSE

• Applicant: Professor Dr. Stefan Dreizler, since 9/2017
• Subject Area: Astrophysics and Astronomy
• Term: from 2017 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 364959081

For a long time globular clusters have been recognized as simple objects - consisting of a single stellar population that was formed several billion years ago. However, over the last years high-resolution photometric and spectroscopic studies have shown that at least two stellar populations exist in almost all globular clusters. This discovery raised new questions - for example, if the different populations show distinct dynamical properties. Despite the short relaxation times of most clusters, there is evidence that the abundance of binary stars is lower in the second compared to the primordial population. It is not only the question of multiple populations where binary stars play an important role for our understanding of globular clusters. Another example is their influence on the timescale at which the cluster undergoes core collapse. In addition, binaries allow one to inverstigate the spatial distribution of stellar remnants, such as neutron stars or black holes. Their distributions strongly affect the central kinematics of the clusters and hence are important to answer the question if globular clusters host intermediate-mass black holes. With masses in the range of 100 to 10,000 solar masses, these objects would fill the gap between stellar black holes and the supermassive ones that are found in the centres of galaxies. Answering the questions raised above is only possible by acquiring large spectroscopic samples of cluster stars. As a member of the consortium that built the Multi Unit Spectroscopic Explorer (MUSE), we have not only participated in the construction of this instrument over the last decade, but have also invested significant work into the preparation of the guaranteed observing time (GTO) granted to the consortium. Our focus in this respect was the development of techniques that strongly enhance the efficiency of spectroscopic observations in globular clusters. This work now allows us to obtain and analyse samples of 10,000 stars per cluster in moderate observing times. Currently we are conductiong a large programme (about 100 hours of observing time) that targets 25 Galactic globular clusters with the aim of answering the following questions: Do intermediate black holes exist in the centers of globular clusters? If yes, how are their properties connected to the cluster properties? What is the binary fraction in globular clusters? How does the fraction vary with cluster properties? How does it vary radially within the cluster? Does it vary with the stellar population?

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Dr. Sebastian Kamann, until 8/2017