Divergent Evolution of Radial Metallicity Gradients in the Thin and Thick Disks of the Milky Way
arXiv:2607.07394
The paper analyzes radial metallicity gradients in the Milky Way's thin and thick disks using over 200,000 red clump stars, finding a strong negative gradient in the thin disk that weakens with height and age, while the thick disk shows a weakly positive, age‑independent gradient.
Abstract
Using 200,388 red clump stars from LAMOST and APOGEE, we investigate the radial metallicity gradients of the Galactic disk as a function of vertical height and stellar age. The thin disk displays a pronounced negative radial metallicity gradient near the Galactic mid-plane that progressively flattens with increasing , following = 0.0784 0.0776 (1 exp ( /1.42)). The thin disk also exhibits a clear age dependence in radial metallicity gradients, evolving smoothly from a strong gradient regime for young stars to a weak gradient regime for old stars, following = 0.0438 0.0233 tanh (( 11.29)/4.21). The thick disk shows weakly positive radial metallicity gradients that remain statistically invariant with respect to both vertical height and stellar age, following respectively, = 0.0038 0.0009 and = 0.0146 0.0007 . These results indicate that the thin disk retains radial metallicity gradients shaped by relatively ordered inside-out growth and long-term secular evolution processes. The thick disk exhibits spatially and temporally homogeneous radial metallicity gradients, which are consistent with a formation environment characterized by mergers of gas-rich systems and/or the turbulent ISM.
7 pages, 7 figures, accepted for publication in ApJL