In recent years, the study of early disc formation and evolution has gained significant momentum, driven by the extraordinary capabilities of three cutting-edge observatories : ALMA, JWST, and Gaia. ALMA and JWST are now delivering detailed measurements of gas kinematics and chemical abundances for hundreds of high-redshift disc galaxies. JWST, in particular, is also producing exquisite rest-frame infrared images, revealing intricate structural features. Strikingly, many of these distant galaxies are gas-rich and already exhibit well-defined bars and spiral arms - structures traditionally associated with more evolved systems. Since most galaxies, including our own, are thought to have passed through such a gas-rich phase, understanding these processes is essential.

In parallel, Gaia’s detailed mapping of the Milky Way has revealed compelling evidence for ancient, thick and thin stellar discs that may date back to the early stages of galaxy formation. Insights are also emerging from local galaxy surveys targeting Milky Way analogues - nearby galaxies with similar properties - which provide valuable external perspectives on our own Galactic history. Collectively, these observations offer tantalizing clues that our understanding of disc galaxy formation and evolution remains incomplete. These developments are further complemented by major strides in simulations of Milky Way-like galaxies, both in controlled experiments and within fully cosmological contexts, enabling us to test theoretical predictions with unprecedented precision.

A key theme to explore is Galactic ecology - the long-term interplay between gas and stars across cosmic time. In gas-poor galaxies, stars tell gas how to move ; in gas-rich galaxies, the reverse is true. What traces remain from these early gas-rich phases ? Can gas clouds scatter stars ? Are some stars born “hot,” with significant random motion ? How do mergers impact gas-rich discs ? Do spiral arms arise primarily from stellar dynamics, gas physics, or the coupling between them ? What role does bar formation play in shaping a galaxy, and how does its evolution unfold ? And how are stellar processes - such as resonant interactions, scattering, radial migration, bar-driven dynamics, or spiral arm formation - modified by the presence of a high gas fraction ?

These are some of the central questions we aim to tackle in this invited workshop, with the goal of advancing a unified picture of disc galaxy evolution.

SOC
Jonathan Bland-Hawthorn (University of Sydney)
Paola Di Matteo (Observatoire de Paris-PSL)
Misha Haywood (Observatoire de Paris-PSL)
Chervin Laporte (CNRS, France)

LOC
Pierre Boldrini
Paola Di Matteo
Misha Haywood
Chervin Laporte
Anna Parul
Alexis Quintana