Young massive star clusters in 3D - spectrophotometric mapping with MUSE

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Most stars form in clustered environments, of which the majority dissolve within a few million years forming the Galactic field population. The densest and most massive star clusters have the potential to remain gravitationally bound and might be long-lived. The physical processes and interactions between the stellar cluster population and its parental HII region are not very well understood. The properties of the majority of these young massive star clusters (YMCs) are difficult to access due to their location in other galaxies. This makes the Galactic YMCs important objects to study, yet, compared to starburst galaxies, YMCs are rare in the Milky Way (MW). For the first time, new instruments and telescopes make it possible to perform detailed, large scale spectroscopic surveys with a reasonable amount of telescope time.For the proposed two-year research project, I plan to perform a study of YMCs, specifically Westerlund 2 (Wd2), using data obtained with the integral field spectrograph MUSE to gain, for the absolute first time, a conclusive insight into the 3D structure, formation, present status, and future evolution of such a YMC. With an age of 1 – 2 Myr at a distance of 4 kpc, Wd2 is the second most massive YMC in the MW (total stellar mass: 37000 solar masses). This highly mass segregated YMC hosts a fully intact upper main sequence and is built from two coeval sub-clumps. These properties, the numerous OB stars, and the surrounding HII region makes Wd2 a perfect test bed to study the interactions of YMCs with their parental molecular gas cloud. Together with the existing deep, multi-epoch Hubble Space Telescope photometry this new instrument gives me the unique opportunity to simultaneously observe and examine the stellar population and the remaining gas to study their feedback and interactions. Determining the velocity dispersion of a large sample of cluster stars will provide information about massive clusters and their long-term stability toward internal and external influences, such as supernova explosions and gravitational interactions with giant molecular clouds or the Galactic disk. I will also address the question on how much the far ultra-violet flux of the OB stars impact the disk dispersal of protostellar disks around low-mass PMS stars. Faster dispersing disks mean that the low-mass stars will grow less in mass, which alters the stellar mass function of the cluster impacting the long-term stability.This project will help to adjust the initial parameters of N-body simulations to trace the long-term evolution of massive clusters over a significant fraction of a Hubble time. These simulations are essential to get a step closer to understand the link between the observed YMCs and the old globular cluster population. I will use Wd2 as an example case to develop new methods for reducing and analyzing such datasets, which will be extended to other YMCs in the MW and the more distant and more massive ones in the Magellanic Clouds.