Turning Points in the Age-Metallicity Relations -- Created by Late Satellite Infall and Enhanced by Radial Migration

TL;DR

This study uses cosmological simulations to show how late satellite infall and radial migration influence the shape of the age-metallicity relation in the Milky Way, creating observable turning points.

Contribution

It demonstrates that late satellite infall, similar to Sagittarius dwarf, causes turning points in the AMR, a novel insight into galactic chemical evolution.

Findings

Turning points in the AMR are signatures of late satellite infall.

Radial migration widens the metallicity range at the AMR turning points.

Simulated AMR features match those observed in the Milky Way.

Abstract

The present-day Age-Metallicity Relation (AMR) is a record of the star formation history of the Galaxy, as this traces the chemical enrichment of the gas over time. We use a zoomed-in cosmological simulation that reproduces key signatures of the Milky Way (MW), g2.79e12 from the NIHAO-UHD project, to examine how stellar migration and satellite infall shape the AMR across the disk. We find in the simulation, similar to the MW, the AMR in small spatial regions (R, z) shows turning points that connect changes in the direction of the relations. The turning points in the AMR in the simulation, are a signature of late satellite infall. This satellite infall has a mass radio similar as that of the Sagittarius dwarf to the MW (~ 0.001). Stars in the apex of the turning points are young and have nearly not migrated. The late satellite infall creates the turning points via depositing metal-poor gas in the disk, triggering star formation of stars in a narrow metallicity range compared to the overall AMR. The main effect of radial migration on the AMR turning points is to widen the metallicity range of the apex. This can happen when radial migration brings stars born from the infallen gas in other spatial bins, with slightly different metallicities, into the spatial bin of interest. These results indicate that it is possible that the passage of the Sagittarius dwarf galaxy played a role in creating the turning points that we see in the AMR in the Milky Way.