The Alpha-element knee of the Sagittarius Stream

TL;DR

This study detects the alpha-element knee in the Sagittarius stream using SDSS/SEGUE data, revealing insights into the galaxy's chemical evolution and its contribution to the Milky Way's halo.

Contribution

First detection of the alpha-element knee in Sagittarius, providing new constraints on its chemical evolution and its role in galactic assembly.

Findings

Alpha-element distribution forms a narrow sequence with a clear turn-down.

The alpha-knee occurs at [Fe/H]=-1.27±0.05 in Sagittarius.

Sagittarius-like galaxies may have contributed to the Milky Way's stellar halo.

Abstract

We employ abundances from the Sloan Digital Sky Survey (SDSS) and the Sloan Extension for Galactic Understanding and Exploration (SEGUE) to study the alpha-element distribution of the stellar members of the Sagittarius stream. To test the reliability of SDSS/SEGUE abundances for the study of Sagittarius, we select high-likelihood samples tracing the different components of the Milky Way, and recover known literature alpha-element distributions. Using selection criteria based on the spatial position, radial velocity, distance and colours of individual stars, we obtain a robust sample of Sagittarius-stream stars. The alpha-element distribution of the Sagittarius stream forms a narrow sequence at intermediate metallicities with a clear turn-down, consistent with the presence of an alpha-element "knee". This is the first time that the alpha-element knee of the Sagittarius dwarf galaxy has been detected. Fitting a toy model to our data, we determine that the alpha-knee in Sagittarius takes place at [Fe/H]=-1.27pm0.05, only slightly less metal-poor than the knee in the Milky Way. This indicates that a small number of Sagittarius-like galaxies could have contributed significantly to the build-up of the Milky Way's stellar halo system at ancient times.