The Hubble sequence, the division of galaxies into star-forming discs and quiescent spheroids, is one of the most iconic observations in astronomy, yet its physical origin remains deeply contested. Are morphological transformation and quenching driven by the same process, or do they merely correlate?
In this talk I will present a comprehensive study of morphological evolution across the star-forming and quiescent galaxy populations in the EAGLE cosmological simulation, tracing the co-evolution of galaxy size, disc-to-total ratio, and three-dimensional shape alongside star formation and black hole growth from early universe to the present day. By decomposing the galaxy population by merger history, I will show that the morphology--quenching connection is not driven by a single channel, but arises through multiple physically distinct pathways that leave characteristic and observable imprints on galaxy structure. In particular, I will highlight a surprising and internally-driven route to quiescence that operates without mergers, and discuss what the three-dimensional shapes of galaxies reveal about how they formed and died.
