Potential Impact of the Sagittarius Dwarf Galaxy on the Formation of Young O-rich Stars

TL;DR

This study investigates how the Sagittarius dwarf galaxy's accretion event influenced the formation of young oxygen-rich stars in the Milky Way, revealing chemical signatures and star formation bursts linked to this interaction.

Contribution

It provides new chemical evidence and analysis linking the Sagittarius dwarf galaxy's infall to recent star formation and oxygen enrichment in the Milky Way's disc.

Findings

Identification of a V-shaped age-metallicity structure in local disc stars.

Detection of a star formation burst between 4 and 2 Gyr ago.

Evidence of increased oxygen abundance and young O-rich stars formed in the outer disc.

Abstract

The Milky Way underwent significant transformations in its early history, characterised by violent mergers and satellite galaxy accretion. However, recent observations reveal notable star formation events over the past 4 Gyr, likely triggered by perturbations from the Sagittarius dwarf galaxy. Here, we present chemical signatures of this accretion event, using the [Fe/H] (metallicity) and [O/Fe] (oxygen abundance) ratios of thin-disc stars. In the normalised age-metallicity plane, we identify a discontinuous V-shape structure at z$_{\rm max}$ (maximum vertical distance from the disc plane) $<$ 0.4 kpc in the local disc, interrupted by a star formation burst between 4 and 2 Gyr ago. This event is characterised by a significant increase in oxygen abundance, resulting in a distinct [O/Fe] gradient and the formation of young O-rich stars. These stars have larger birth radii, indicating formation in the outer disc followed by radial migration to the Solar neighbourhood. Simulations of late satellite infall suggest that the passage of the Sagittarius dwarf galaxy may have contributed to the observed increase in oxygen abundance in the local disc.