The AMBRE Project: Solar neighbourhood chemodynamical constraints on Galactic disc evolution

Context. The abundance of alpha-elements relative to iron ([alpha/Fe]) is an important fossil signature in Galactic archaeology for tracing the chemical evolution of disc stellar populations. High-precision chemical abundances, together with accurate stellar ages, distances, and dynamical data, are crucial to infer the Milky Way formation history. Aims. The aim of this paper is to analyse the chemodynamical properties of the Galactic disc using precise magnesium abundance estimates for solar neighbourhood stars with accurate Gaia astrometric measurements. Methods. We estimated ages and dynamical properties for 366 main sequence turn-off stars from the AMBRE Project using PARSEC isochrones together with astrometric and photometric values from Gaia DR2. We use precise global metallicities [M/H] and [Mg/Fe] abundances from a previous study in order to estimate gradients and temporal chemodynamic relations for these stars. Results. We find a radial gradient of -0.099 +/- 0.031 dex kpc(-1) for [M/H] and +0.023 +/- 0.009 dex kpc(-1) for the [Mg/Fe] abundance. The steeper [Mg/Fe] gradient than that found in the literature is a result of the improvement of the AMBRE [Mg/Fe] estimates in the metal-rich regime. In addition, we find a significant spread of stellar age at any given [Mg/Fe] value, and observe a clear correlated dispersion of the [Mg/Fe] abundance with metallicity at a given age. While for [M/H]