The ERC program ArcheoDyn consists of three projects. The first and second projects employ the stellar fossil record inside globular clusters (GCs) within the Milky Way, whereas the third project uses GCs as living fossils of the hierarchical build-up of galaxies.
Project 1: Robust dynamical inference of intermediate-mass black holes in globular clusters
We explored a sample of high-end Monte Carlo simulations of GCs, with and without a central IMBH, to investigate to what degree commonly-used dynamical models can infer an IMBH. We found that these models are reliable for a high-mass IMBH, but they lack the sensitivity to measure a low-mass IMBH. In parallel, we showed that an IMBH will not only halt the segregation of stellar binaries towards the cluster center, but also, directly and indirectly, disrupt the binaries that segregate. We thus predict that GCs with a relatively low fraction of binaries in the core and/or where the central velocity dispersion is not artificially increased due to binaries, are strong candidates to host an IMBH. With the crucial and novel insights achieved, we are now in the ideal position to robustly infer the presence of IMBHs in GCs.
Project 2: Dynamically uncovering the origin of multiple populations in globular clusters
Three sets of results have successfully been completed related to this project. Firstly, a detailed analysis and modeling of the kinematics, ages and metallicities of several thousand stars in the globular cluster M54 revealed the presence of a centrally concentrated metal-rich young population which likely formed as the result of a strong tidal interaction with the Milky Way. Secondly, population-dynamical modeling of the GC M80 suggests that the three chemically-distinct populations must have formed with primordial kinematic differences: a novel constraint on the origin of this phenomenon. Thirdly, development and validation of our new population-orbit modeling. First applications to nearby galaxies already yield high-impact results and promise further insights when using the latest GC datasets.
Project 3: Dynamically recovering satellite galaxy mergers via their surviving globular clusters
The problem is being tackled from different and complementary sides: combining (1) theoretical studies on the information needed to recover the gravitational potential with accreted globular clusters, (2) simulations to develop, verify, as well as understand the caveats in novel methodologies, and (3) observations to gain insight into the formation histories of individual galaxies. This multi-faceted approach already yielded several new insights. Firstly, with a sample of more than 150 GCs the dark matter halo properties are well recovered and even the shape can be constrained to be non-spherical. Secondly, combining high-quality dataset of velocities and metallicities of hundreds of GCs with detailed stellar population analysis of nuclear star clusters (NSCs) establishes a transition in the dominant NSC formation channel with galaxy mass: NSCs in low-mass galaxies predominantly grow through the inspiral of GCs, while central star formation can contribute to NSC growth in more massive galaxies. Combining our model that explains the latter transition with our novel method to unveil a galaxy's accretion history from an integrated-light spectra, will enable us to infer the assembly history, including ancient satellite mergers, of individual galaxies.
