Present-day disk galaxies, including the Milky Way, exhibit two distinct structures: an older thick disk and a younger thin disk. However, the timing and mechanisms of their formation remain open questions, primarily due to observational limitations — these structures had not been identified beyond z=0 until recently. Leveraging JWST’s superb capabilities, we have, for the first time, identified and investigated thin and thick disks across cosmic time, up to 10 Gyr ago. Our study reveals a consistent trend: in the earlier universe, more galaxies appear to have had only a single thick disk, while in later epochs, more galaxies showed a two-layered structure with an additional thin disk component. This suggests a sequential formation, in which galaxies first formed a thick disk, followed by the development of a thin disk embedded within it. Notably, thin disks formed earlier in more massive galaxies (disk downsizing). By linking disk structural properties with gas kinematics, we propose that the Toomre Q regulated disk formation naturally explains disk downsizing and disk geometric properties. Complementing this, ALMA observations probing the thick disk formation epoch z~4-5 allow us to investigate how thick disks may have formed in gas-rich systems. I will present how such formation likely proceeded through dynamical processes, such as stellar scattering driven by disk substructures common in gas-rich disks, as supported by observations and numerical simulations.
Contact local et organisateur : Emanuele DADDI
DAp