Turbulent Gas-rich Disks at High Redshift: Origin of Thick Stellar Disks Through 3D “Baryon Sloshing”

In response to recent observations from JWST and Atacama Large Millimeter Array, we explore a new class of dynamically self-consistent models that mimics a plausible progenitor of the Milky Way over a wide range of disk gas fractions, f gas . The high gas surface densities encourage vigorous star formation, which in turn couples with the gas to drive turbulence. We show that this coupling through momentum recoil drives a random walk of the baryonic potential minimum with respect to total gravitational potential, Φ tot ( R , ϕ , z ). The amplitude of the bulk motion depends on the feedback strength, which in turn is directly associated with f gas . At its most extreme, when gas is the sole contributor to the disk potential ( f gas = 100%), the amplitude of the walk can reach up to R ≈ 5 kpc within Φ tot . The disk dominates over dark matter ( f disk ≳ 50%) within R s = 2.2 R disk , where R disk is the exponential disk scale length. For a lower f disk and/or f gas , the 3D sloshing amplitude and velocity are reduced. The combination of strong feedback and sloshing leads to the newly formed stars being dynamically heated and settling to a more spatially extended disk population. The 3D heating process is roughly isotropic but its effects are more noticeable in ∣ z ∣ due to the initial dynamical coldness of the star-forming disk. Such a disk has enhanced [ α /Fe] stellar abundances and a vertical (but no radial) gradient in stellar age and metallicity, both consistent with the Milky Way’s thick stellar disk.