“Spiral arms in stellar and gaseous disks: engines of galaxy morphological transformation”
Spirals are iconic features of galaxies, and yet conventional theoretical models for how they emerge and evolve only partially capture their observed traits and their connections to their host disks. Recent JWST observations of beautiful, regular spiral patterns at redshifts z~2 and beyond underscore the need to resolve these theoretical shortcomings. I will present a new picture of spiral patterns as short-lived density waves, analytically bridging the gap between the conventional long-lived density wave picture and the model of spirals as transient material patterns. This new view forces a wholesale revisioning of how spirals influence their host galaxies: rather than merely reflecting conditions in the underlying disk, collectively excited spirals actively shape it, producing widespread changes in galaxy structure through dynamical heating and changes in angular momentum. I will describe how these widespread changes are the very ingredients that give rise to global spiral patterns and naturally lead to stellar bulge growth, radial gas inflows and an overall structural compaction over cosmic time. The picture of global, collective spiral excitation also has implications for the kinematics and the rich structure of gas disks, as revealed by JWST/MIRI imaging of nearby galaxies. These structures suggest a simple unified model in which radial gas flows appear alongside dynamical heating, and the latter acts as an important source of turbulent motion to offset dissipation.