The properties of galaxies considerably change across cosmic time while still following the well-established scaling relations all in place at z = 0 out to z ~ 9, such as the galaxy mass vs. star formation rate (referred to as the main sequence of galaxies), the galaxy mass vs. metallicity, and the star formation rate vs. gas content available to create the next generation of stars (the Schmidt-Kennicutt relation). This tells us that the process of formation of stars and their associated feedback play a vast regulator role in galaxy evolution. To really link star formation and feedback to galaxy evolution one needs to resolve the units of star formation in galaxies.

The exquisite spatial resolution provided by JWST when combined with strong gravitational lensing, plays a pivotal role because it allows to access the parsec scales that are relevant for probing the star formation process by resolving the rest-frame UV/optical emission of galaxies down to few tens of parsecs. The JWST images reveal the clumpy morphology of galaxies out to z ~ 12. Thousands of these ubiquitous clumps have already been studied and they ended to be associated with individual massive star clusters, star cluster associations, HII regions, and star-forming complexes depending on their sizes, and in rare cases with globular clusters. With, on average, their 10 times larger sizes, the clumps reach mass surface densities of local massive star clusters and even globular clusters. These high densities likely arise from the higher ambient ISM pressure in high-redshift galaxies. Clumps also show a clear increase of their SFR surface density with redshift, supporting the enhanced contribution of the clustered star-formation to the integrated SFR of the host galaxies. Clumps account for 20-60% of the stellar mass of their host galaxy. Pioneering studies with ALMA reveal extreme conditions (high masses and mass surface densities) for giant molecular clouds (GMCs) where stars will form. With combined HST/JWST and ALMA data sets, we are starting to build a picture of the star-formation cycle in high-redshift galaxies revealing a possible enhancement in the star-formation efficiency at GMC scale up to ~30% by z ~ 1. Numerical simulations face the challenge of reproducing all the pieces of knowledge current observations can provide and recreating a picture of galaxies from their formation to their evolution including the clumpy structure.

It is very timely to bring the observational and theoretical communities altogether during this Special Session SS5 to discuss: the role of clumps in the star formation and mass assembly of galaxies throughout the cosmic time; the link of clumps to the physical, morphological, and kinematical properties of their host galaxies; and the simulation perspectives on clump formation mechanisms in evolving galaxies to understand how we can use clumps as tracers of galaxy evolution.

Programme

• Characterisation of stellar clumps and star clusters: their properties and their role in star formation and feedback of early galaxies.
• Stellar clump and star cluster population demographics: their link to the host galaxy physical conditions and globular clusters.
• Simulation perspectives on stellar clump and star cluster formation mechanisms in evolving galaxies: are they building-blocks of galaxy assembly?

Invited speakers

Scientific organisers

Miroslava Dessauges-Zavadsky (Geneva University, Switzerland), Angela Adamo (Stockholm University, Sweden), Lucio Mayer (Zurich University, Switzerland), Johan Richard (CRAL Lyon, France), Eros Vanzella (INAF Bologna,Italy)

Contact

Miroslava Dessauges-Zavadsky