Unveiling the time evolution of chemical abundances across the Milky Way disc with APOGEE

Abstract

ABSTRACT Chemical abundances are an essential tool in untangling the Milky Way’s enrichment history. However, the evolution of the interstellar medium abundance gradient with cosmic time is lost as a result of radial mixing processes. For the first time, we quantify the evolution of many observational abundances across the Galactic disc as a function of lookback time and birth radius, $\rm \text{R}_\text{birth}$. Using an empirical approach, we derive $\rm \text{R}_\text{birth}$ estimates for 145 447 APOGEE DR17 red giant disc stars, based solely on their ages and $\rm [Fe/H]$. We explore the detailed evolution of six abundances [Mg, Ca (α), Mn (iron-peak), Al, C (light), Ce (s-process)] across the Milky Way disc using 87 426 APOGEE DR17 red giant stars. We discover that the interstellar medium had three fluctuations in the metallicity gradient ∼9, ∼6, and ∼4 Gyr ago. The first coincides with the end of high-α sequence formation around the time of the Gaia–Sausage–Enceladus disruption, while the others are likely related to passages of the Sagittarius dwarf galaxy. A clear distinction is found between present-day observed radial gradients with age and the evolution with lookback time for both [X/Fe] and [X/H], resulting from the significant flattening and inversion in old populations due to radial migration. We find the $\rm [Fe/H]$–$\rm [\alpha /Fe]$ bimodality is also seen as a separation in the $\rm \text{R}_\text{birth}$–$\rm [X/Fe]$ plane for the light and α-elements. Our results recover the chemical enrichment of the Galactic disc over the past 12 Gyr, providing tight constraints on Galactic disc chemical evolution models.