[Mg/Fe] ratios in the solar neighbourhood: stellar yields and chemical evolution scenarios

TL;DR

This study uses new precise [Mg/Fe] data from the AMBRE:HARPS dataset to evaluate chemical evolution models of the Milky Way's disc, highlighting the challenges in reproducing observed abundance trends and the importance of stellar migration and formation history.

Contribution

It provides a detailed comparison of chemical evolution models with new observational data, emphasizing the limitations of current stellar yields and the role of different formation scenarios.

Findings

Semi-empirical yields best fit the data for thick and thin discs.

Models struggle to reproduce the high-metallicity and low-metallicity tails.

Radial migration helps explain the tails of the [Mg/Fe] distribution.

Abstract

Context. The [Mg/Fe] abundance ratios are a fundamental fossil signature to trace the chemical evolution of the disc. Despite of the huge observational and theoretical effort, discrepancies between models and data are still present and several explanations have been put forward to explain the [$\alpha$/Fe] bimodality. Aims. In this work, we take advantage of a new AMBRE:HARPS dataset, which provides new and more precise [Mg/Fe] estimations, as well as reliable stellar ages for a subsample of stars, to study the evolution of the solar neighbourhood. Methods. The above data are compared with detailed chemical evolution models for the Milky Way, exploring the most used prescriptions for stellar yields and different formation scenarios for the Galactic disc, i.e. the delayed two-infall and the parallel model, also including prescriptions for stellar radial migration. Results. We see that most of the stellar yields struggle to reproduce the observed trend of the data and that semi-empirical yields are still the best to describe the [Mg/Fe] evolution in the thick and thin discs. In particular, most of the yields still predict a steeper decrease of the [Mg/Fe] ratio at high metallicity than what is shown by the data. The bulk of the data are well reproduced by the parallel and two-infall scenarios, but both scenarios have problems in explaining the most metal-rich and metal-poor tails of the low-$\alpha$ data. These tails can be explained in light of radial migration from inner and outer disc regions, respectively. Conclusions. Despite of the evidence of stellar migration, it is difficult to estimate the actual contribution of stars from other parts of the disc to the solar vicinity. However, the comparison between data and models suggests that peculiar histories of star formation, such as that of the two-infall model, are still needed to reproduce the observed distribution of stars.