Abstract

Most disc galaxies go through an early epoch of being “gas rich,” an era that is being actively explored today through ALMA and JWST observations. This high gas-fraction phase got going much sooner (z > 3) than anticipated by cosmological N-body simulations. A new class of controlled (Nexus) simulations of these early times reveals that these turbulent discs have extraordinary properties. Unexpectedly, spiral arms, stellar and gaseous bars, even bulges, all form under these conditions. Moreover, baryon sloshing in 3D driven by strong feedback gives rise to thick stellar discs. We argue this is the most likely origin of alpha-enriched thick stellar discs observed today. The sloshing gives rise to specific signatures that may already be observable in ALMA data. We discuss the implications of the new work on galaxy studies.