ODYSSEY · Old anD Young Star clusterS tracing Evolution and assemblY

In the standard framework of galaxy evolution, galaxies form in a two-phase scenario that comprises a quasi-monolithic formation of an in-situ population, followed by the accretion of of lower-mass galaxies. As these merger processes significantly alter the morphology and kinematic state of a galaxy, reconstructing the assembly history of galaxies is a challenging but fundamental task to understand galaxy evolution. In that context, dense star clusters such as globular clusters, young massive clusters, and nuclear star clusters, that still contain information of their birthplace and subsequent evolution imprinted in their stellar population are potentially powerful tracers of galaxy assembly. While ancient globular clusters are fossil records of early star formation and galaxy accretion, young massive star clusters trace recent star formation episodes and interactions, and nuclear star clusters provide an unique window into the evolution of a galaxy's central region. The ODYSSEY action aims to fully unlock the potential of these star clusters as tracers of galaxy evolution by employing a comprehensive framework that combines for the first time the insights provided by globular clusters, young massive clusters and nuclear clusters. To achieve this, ODYSSEY has two main objectives: 1) exploring the complex interplay between galaxies and the star clusters they host and b) constructing a flexible semi-analytical model that constrains the assembly history of individual galaxies from their star clusters. The proposed research programme will greatly advance our understanding of the mechanisms that shape star clusters and of how they are connected to the evolution of their host galaxies, while at the same time providing a new methodology of how galaxy evolution can be studied.