Revisiting the Galactic age–metallicity relation from wide white dwarf–main-sequence binaries

Context. The age–metallicity relation (AMR) is a fundamental observational constraint for understanding the chemical evolution of the Galaxy. As reliable cosmochronometers, white dwarfs in binary systems with main-sequence companions (WD+MS binaries) provide excellent laboratories to study this relation since both components are expected to be coeval. Aims. We constructed a sample of widely separated WD+MS binaries using data from the third data release of the Gaia mission in order to investigate the AMR of the Galactic disk. Methods. The sample is identified using photometric measurements and parallaxes of both components. White dwarf ages were derived by interpolating their Gaia absolute G magnitudes and Gaia BP-RP colours within state-of-the-art white dwarf evolutionary sequences. We compiled publicly available [Fe/H] abundances for the main-sequence companions from the literature and combined them using different statistical approaches to obtain representative metallicity values for each system. Results. We derived the AMR from several sub-samples of WD+MS that use independent measurements of [Fe/H] abundances and consistently find a large dispersion in [Fe/H] at all ages. This behaviour agrees with previous determinations of the AMR based on WD+MS binaries and on samples of isolated stars. Conclusions. Our results reinforce the observational evidence that the AMR in the Galactic disk exhibits substantial intrinsic scatter, likely reflecting the combined effects of multiple mechanisms such as radial migration, inhomogeneous chemical enrichment, and variations in the star formation history.