This project MATRYOSHKA (Mass Assembly TRaced bY glObular clusterS, tHe Key to gAlaxy evolution) aims to address three key questions in astrophysics: (i) how do galaxies grow in size and mass; (ii) what is the dark matter content of these galaxies; and (iii) whether the current cosmological paradigm is compatible with this picture. We propose to approach these problems in a novel way by leveraging our expertise of some of the oldest objects in the universe globular clusters and the stellar content in galaxies. We thus aim at using globular clusters as the master key to unlock the different contributions of the scales of our Universe, each constituting a fundamental layer for the next one, like a matryoshka doll.
For a sample of nearby galaxies (<10 Mpc), we will identify ex-situ accretions by obtaining detailed chemical abundances and mass-to-light ratios of their globular clusters. This will be the first systematic attempt to use globular clusters to constrain the degree of accretion in the halos of galaxies beyond the Milky Way. Moving further afield (<50 Mpc), we will exploit the wealth of archival integral field spectroscopic data available (primarily MUSE@VLT), combined with state-of-art spectral deconvolution techniques, to explore the central stellar populations, nuclear star clusters and, for the first time, the very central globular cluster populations for a large sample of massive galaxies. At the same time, we will use archival (primarily HST) and new data to determine the accreted mass fractions for an overlapping galaxy sample by mapping globular cluster colour distributions to accreted baryonic and dark matter mass via Monte Carlo merger models. But besides understanding the general galaxy population, we will also focus on extreme galaxies, including ultra-diffuse galaxies, dwarfs and massive compact galaxies.
Pushing to cosmological distances, we propose to explore the evolution of globular clusters as a function of redshift. Leveraging archival James Webb Space Telescope data for lensed systems for z>1, where globular clusters are now being identified in increasing numbers, we aim to construct ageredshift relations by age-dating the clusters via SED fitting. This will be among the first attempts to use globular clusters historically used to establish a lower limit on the age of the Universe to age-date the Universe as a function of redshift, and thereby constrain cosmological parameters including the Hubble constant, the dark matter density and the equation of state.
The foundation of this proposal will be the production of a new suite of stellar population synthesis models (based on E-MILES) which will be specifically tailored for globular clusters, taking into account their unique chemistry and stellar mass functions. This will allow us to assess the impact of the systematics of the models on the above astrophysical problems in a controlled way, and will allow us to unlock the potential of globular clusters to understand key problems in galaxy formation and cosmology. The research team in MATRYOSHKA, formed with experts in globular cluster studies, galaxy stellar populations, dynamics and stellar populations synthesis modelling, is thus ideally poised to pursue such an ambitious Project.
