The Age-Metallicity Relation in the Solar Neighbourhood

Abstract: Age-metallicity relation for the Galactic disc is a crucial tool and to constrain the Galactic chemical evolution models. We investigate the age-metallicity relation of the Galactic disc using the red giant branch stars in the Solar neighbourhood. The data cover the Galactocentric radius of $7\leq R_{\rm gc} (\rm kpc) \leq9.5$, but extends up to 4 kpc in height from the Galactic plane. We use kinematic age derived from highly precise astrometric data of Gaia Data Release 2 and element abundance ratios from high-resolution spectroscopic data of APOGEE-2 catalogues. We apply a two-component Gaussian mixture model to chemically separate the programme stars into thin and thick disc populations. The stars in each population are grouped into different distance intervals from the Galactic plane. The mean metal abundances and velocity dispersions of the stars in the groups were calculated and the kinematic ages were determined from their kinematic parameters. We found a steep relation for the thin disc with -0.057$\pm$0.007 dex Gyr$^{-1}$, and even a steeper value of -0.103$\pm$0.009 dex Gyr$^{-1}$ for the thick disc. These age-metallicity relations along with the prominent differences in age, metallicity, and kinematic behaviours seen from the data, clearly show it is important to consider the distinct formation scenarios of the Galactic disc components in modelling the Milky Way.