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

TL;DR

This study analyzes the evolution of chemical abundances in the Milky Way disk over 12 billion years using APOGEE data, revealing fluctuations in metallicity gradients and the impact of radial migration on observed abundance patterns.

Contribution

First to quantify the evolution of multiple chemical abundances across the Galactic disk as a function of lookback time and birth radius using a large APOGEE dataset.

Findings

Identified three fluctuations in the metallicity gradient at ~9, ~6, and ~4 Gyr ago.

Discovered the separation of the [Fe/H]--[$ ext{α}$/Fe] bimodality in the $R_ ext{birth}$--[X/Fe] plane.

Revealed the effects of radial migration on the observed abundance gradients over time.

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 disk as a function of lookback time and birth radius, $R_\text{birth}$. Using an empirical approach, we derive $R_\text{birth}$ estimates for 145,447 APOGEE DR17 red giant disk stars, based solely on their ages and [Fe/H]. We explore the detailed evolution of 6 abundances (Mg, Ca ($\alpha$), Mn (iron-peak), Al, C (light), Ce (s-process)) across the Milky Way disk using 87,426 APOGEE DR17 red giant stars. We discover that the interstellar medium had three fluctuations in the metallicity gradient $\sim 9$, $\sim 6$, and $\sim4$ Gyr ago. The first coincides with the end of high-$\alpha$ 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 [Fe/H]--[$\alpha$/Fe] bimodality is also seen as a separation in the $R_\text{birth}$--[X/Fe] plane for the light and $\alpha$-elements. Our results recover the chemical enrichment of the Galactic disk over the past 12 Gyr, providing tight constraints on Galactic disk chemical evolution models.