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

¹ School of Physics and Astronomy, Sun Yat-sen University, Zhuhai 519082, PR China
e-mail: tangbt@mail.sysu.edu.cn, zhangjj239@mail.sysu.edu.cn, yan@nju.edu.cn
² CSST Science Center for the Guangdong-Hong Kong-Macau Greater Bay Area, Zhuhai 519082, PR China
³ School of Astronomy and Space Science, Nanjing University, Nanjing 210093, PR China
⁴ Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, Nanjing 210093, PR China
⁵ Universidad Nacional Autónoma de México, Instituto de Astronomía, AP 70-264, CDMX 04510, México
⁶ Instituto de Astronomía, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta, Chile

Received: 19 May 2022
Accepted: 25 November 2022

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 [α/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 [α/Fe]. The low [Al/Fe] (∼ − 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 ∼ − 2.7, and a minimum Type Ia supernovae delay time of ∼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.