Star clusters near and far: mapping galaxy evolution through parsec scales physical processes

IAP weekly specialised seminars / 20 September 2024

Angela Adamo (Department of Astrononomy, Stockholm University, Sweden)

Thanks to JWST observations of gravitationally lensed regions, we have the opportunity to study at UV and optical restframe young galaxies where very little is known about star formation at 10s parsec scales. In general, galaxies appear to face strong bursts, taking place in compact regions, typically refer to as stellar clumps, where chemical enrichment can be detected. Opposite to what concluded with HST observations, JWST shows that disks are in place already at very high-redshifts with stellar clumps dominating also their optical light. In my talk I will present the recent results we have achieved by studying star clusters and stellar clumps in lensed galaxies with JWST between redshift 1 and 10. We find evidence that clumps between redshift 1 and 5 follow a power-law mass distribution as predicted by in-situ formation scenarios based on disk fragmentation processes. We see clear redshift evolution, with higher clump stellar masses found in disks at cosmic noon, indicative of bulge growth. Clumps become progressively young, dense and show increasing star formation rate densities as a function redshift. When reaching the highest magnification, we can resolve these clumps into star clusters. In particular, I will discuss the physical properties of star clusters detected in reionisation-era galaxies, when proto-globular clusters are thought to form. We find direct evidence of gravitationally bound star clusters already a redshift 10, when the universe was only half billion year old. These proto-globular clusters are very dense, host very massive stars, are located in compact regions, dominate the luminosity and contribute significantly to their host galaxy mass. The observed stellar densities of these proto-GCs open new venues to explore black hole seeds formation and super massive stars via stellar collisions in their cores and thus explain the potential polluters at the origin of chemical enriched stars in globular clusters. Our results indicate that star cluster formation and stellar feedback might be a dominant star formation mode for galaxies in the early universe.