APOGEE Chemical Abundances of the Sagittarius Dwarf Galaxy

TL;DR

This study analyzes the detailed chemical abundances of 158 red giant stars in the Sagittarius dwarf galaxy using APOGEE data, revealing a deficiency in certain elements and supporting a top-light IMF in its star formation history.

Contribution

First high-resolution chemical abundance analysis of multiple elements in Sgr stars, providing new insights into its star formation and initial mass function.

Findings

Sgr stars with [Fe/H] > -0.8 are deficient in elemental ratios compared to the Milky Way.

Evidence supports a top-light IMF in Sgr's past star formation.

Recent Fornax and LMC stars may also have formed with a top-light IMF.

Abstract

The Apache Point Observatory Galactic Evolution Experiment (APOGEE) provides the opportunity to measure elemental abundances for C, N, O, Na, Mg, Al, Si, P, K, Ca, V, Cr, Mn, Fe, Co, and Ni in vast numbers of stars. We analyze the chemical abundance patterns of these elements for 158 red giant stars belonging to the Sagittarius dwarf galaxy (Sgr). This is the largest sample of Sgr stars with detailed chemical abundances and the first time C, N, P, K, V, Cr, Co, and Ni have been studied at high-resolution in this galaxy. We find that the Sgr stars with [Fe/H] $\gtrsim$ -0.8 are deficient in all elemental abundance ratios (expressed as [X/Fe]) relative to the Milky Way, suggesting that Sgr stars observed today were formed from gas that was less enriched by Type II SNe than stars formed in the Milky Way. By examining the relative deficiencies of the hydrostatic (O, Na, Mg, and Al) and explosive (Si, P, K, and Mn) elements, our analysis supports the argument that previous generations of Sgr stars were formed with a top-light IMF, one lacking the most massive stars that would normally pollute the ISM with the hydrostatic elements. We use a simple chemical evolution model, flexCE to further backup our claim and conclude that recent stellar generations of Fornax and the LMC could also have formed according to a top-light IMF.