In local galaxies, JWST wavelengths and sensitivity have opened a unique opportunity to study the emergence phases of star clusters when their stellar feedback is rapidly destroying the natal molecular clouds. We find an evolutionary sequence where photodissociation regions rapidly disappear and leave place to classic HII regions. The 3.3 and 7.7 micron polycyclic aromatic hydrocarbons (PAH) bands appears to be a sensitive tracer of the earliest phases and rapidly disappears within 4 Myr at the location of the emerging star clusters. We find evidence of variations in the timescale for emergence in diverse galactic environments, with an average time scale of 5 Myr, suggesting that SNe will explode in a medium already processed by photoionisation and stellar winds, and have a large impact for the galactic scale interstellar medium (ISM).
At higher-redshift, JWST is providing a unique view of the optical restframe of 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. In contrast to what previously established, JWST shows that disks are in place already at very high-redshifts with stellar clumps dominating also their optical light.
The speaker will present recent results achieved by studying star clusters and stellar clumps in lensed galaxies. Thanks to gravitational telescopes combined with JWST unprecedented sensitivity and resolution we are able to analyse star formation down to 10s of parsec scales. We find evidence that clumps form in-situ from disk fragmentation processes even at redshift beyond 2. They follow a power-law mass distribution and show very high stellar densities. When reaching the highest magnification, we can resolve these clumps into star clusters. Furthermore, the speaker 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 and dominate the luminosity and mass of their host galaxies. These proton-globular clusters are incredible furnaces for the formation of massive stars and stellar black holes, as well as dynamical interactions. Their stellar feedback plays a fundamental role in setting the star formation efficiency and regulate the overall star formation cycle of infant galaxies.