Star-Forming Clumps and Clustered Starbursts across Cosmic Time

5 - 30 October 2020 (postponed to 4 to 28 October 2022)

Anita Zanella, Daniela Calzetti, Bruce Elmegreen, Michael Hilker, Florent Renaud

This program addresses the questions of how starbursting complexes, gaseous high-redshift clumps, giant molecular clouds, and young massive star clusters are formed, what are their physical properties, and what is their impact on galaxy evolution. Current observations and simulations allow us to directly compare how star formation proceeds at low and high redshift, down to the small spatial scales of star clusters. They have shown that local galaxies have modest star formation rates and form the bulk of their stars in giant molecular clouds, producing star complexes in a self-similar hierarchy from individual stars to young massive star clusters. In comparison, galaxies in the early Universe have high star formation rates and host large star-forming regions, dubbed "clumps", 10 – 1000 times larger, brighter, and more massive than local giant molecular clouds, although recent studies suggest that giant clumps may be formed of sub-clumps. An additional piece of the puzzle is represented by globular clusters that show a wide diversity of metallicities which calls for a range of different origins and perhaps even a range of different formation mechanisms. Connecting the origins and physical properties of local giant molecular clouds, young massive star clusters, high-redshift clumps, and globular clusters is paramount to make a step forward in our understanding of clustered star formation in the context of galaxy evolution.
During the program the mornings will be devoted to reviews and contributed talks aimed at bridging these different topics. In the afternoons instead there will be some break-out group sessions focussed on specific open questions aimed at sparking the discussion among researchers with different backgrounds and foster collaborations possibly leading to new ideas for observing and/or computing time projects.

The main topics covered during the program will be the following:

• First week: The impact of galaxy interactions and secular evolution on the formation of star clusters and clumps.
How do giant molecular clouds and young massive clusters form, and can we learn from them, extrapolating to high-redshift clumps? What does the bulge/black hole/globular cluster correlation tell us about secular versus interaction-driven bulge formation? How can we measure the interaction rate at high redshift? What are the main simulations' ingredients determining the formation scenarios of clumps and globular clusters?

• Second week: Connecting low- and high-redshift clustered star formation.
When and why clumps become less common giving way to giant molecular clouds? Does this epoch coincide with the shut off of the globular clusters' formation and are these processes linked? Can we find the 'analogs' of clumps in local galaxies, are they related to giant star forming regions of dwarf galaxies or is the hierarchical structure of stars in spirals an analog/vestige to the clumps? How can simulations consistently study  giant molecular clouds, young star clusters, globular clusters and clumps despite the large range of needed physical scales?

• Third week: The impact of clustered star formation on the evolution of the host galaxy.
What are the processes determining clusters survival and what is the relevance of these mechanisms to the lifetime of giant molecular clouds? What is the evidence that individual clumps migrate to a galaxy center to contribute to the bulge? Can the observations of clumps, such as gas outflows, tell us something about the quenching of star formation in galaxies? How to compare the different feedback recipes in simulations driving to contradictory predictions about star cluster survival and what observables could we use to constrain them?

• Fourth week: Linking clumps and globular clusters.
Could globular cluster seeds be formed in high-redshift clumps? What is the evidence from local galaxies for the initial masses of globular clusters in their two populations (blue and red) and their internal multiple populations (Na/O high and low)? What would be the ideal survey to 'map' globular cluster formation in the early Universe?