Galactic Archaeology with asteroseismic ages: evidence for delayed gas infall in the formation of the Milky Way disc

TL;DR

This study uses asteroseismic ages to constrain models of the Milky Way's formation, finding that a delayed second gas infall best explains observed stellar abundances and ages.

Contribution

It demonstrates that a revised two-infall chemical evolution model with a delay of about 4.3 Gyr accurately reproduces Milky Way disc stellar properties.

Findings

The revised two-infall model matches observed abundance ratios and age distributions.

The parallel formation scenario fails to reproduce the old stellar age distribution.

A delay of approximately 4.3 Gyr in gas infall is essential for accurate modeling.

Abstract

Precise stellar ages from asteroseismology have become available and can help setting stronger constraints on the evolution of the Galactic disc components. Recently, asteroseismology has confirmed a clear age difference in the solar annulus between two distinct sequences in the [$\alpha$/Fe] versus [Fe/H] abundance ratios relation: the high-$\alpha$ and low-$\alpha$ stellar populations. We aim at reproducing these new data with chemical evolution models including different assumptions for the history and number of accretion events. We tested two different approaches: a revised version of the `two-infall' model where the high-$\alpha$ phase forms by a fast gas accretion episode and the low-$\alpha$ sequence follows later from a slower gas infall rate, and the parallel formation scenario where the two disc sequences form coevally and independently. The revised `two-infall' model including uncertainties in age and metallicity is capable of reproducing: i) the [$\alpha$/Fe] vs. [Fe/H] abundance relation at different Galactic epochs, ii) the age$-$metallicity relation and the time evolution [$\alpha$/Fe]; iii) the age distribution of the high-$\alpha$ and low-$\alpha$ stellar populations, iv) the metallicity distribution function. The parallel approach is not capable of properly reproduce the stellar age distribution, in particular at old ages. In conclusion, the best chemical evolution model is the revised `two-infall' one, where a consistent delay of $\sim$4.3 Gyr in the beginning of the second gas accretion episode is a crucial assumption to reproduce stellar abundances and ages.