Near-infrared chemical abundances of stars in the Sculptor dwarf galaxy

TL;DR

This study analyzes near-infrared spectra of 43 stars in the Sculptor dwarf galaxy to determine chemical abundances, revealing insights into its formation history and chemical evolution.

Contribution

First high-resolution NIR abundance measurements of O, Si, and Al in Sculptor stars, and a chemical evolution model indicating a top-light IMF and formation gradients.

Findings

Confirmed lower [$oldsymbol{ extalpha}$/Fe] in dwarf galaxies compared to MW.

Identified low [Al/Fe] as a marker for dwarf galaxy stars.

Detected metallicity and element abundance gradients supporting outside-in formation.

Abstract

Owing to the recent identification of major substructures in our Milky Way (MW), the astronomical community has started to reevaluate the importance of dissolved and existing dwarf galaxies. In this work, we investigate up to 13 elements in 43 giant stars of the Sculptor dwarf galaxy (Scl) using high-signal-to-noise-ratio near-infrared (NIR) APOGEE spectra. Thanks to the strong feature lines in the NIR, we were able to determine high-resolution O, Si, and Al abundances for a large group of sample stars for the first time in Scl. By comparing the [$\alpha$/Fe] (i.e., O, Mg, Si, Ca, and Ti) of the stars in Scl, Sagittarius, and the MW, we confirm the general trend that less massive galaxies tend to show lower [$\alpha$/Fe]. The low [Al/Fe] ($\sim -0.5$) in Scl demonstrates the value of this ratio as a discriminator with which to identify stars born in dwarf galaxies (from MW field stars). A chemical-evolution model suggests that Scl has a top-light initial mass function (IMF), with a high-mass IMF power index of $\sim -2.7$, and a minimum Type Ia supernovae delay time of $\sim 100$ Myr. Furthermore, a linear regression analysis indicates a negative radial metallicity gradient and positive radial gradients for [Mg/Fe] and [Ca/Fe], in qualitative agreement with the outside-in formation scenario.