Estimating Fe and Mg Abundances in the Milky Way Dwarf Galaxies Using Subaru/HSC and DEIMOS

TL;DR

This study uses Subaru/HSC photometry and Keck/DEIMOS spectroscopy to map iron and magnesium abundance gradients in Milky Way dwarf galaxies, revealing insights into their star formation histories and chemical evolution.

Contribution

It introduces a novel method combining photometric data with machine learning to identify giant stars and analyze chemical abundance distributions in dwarf galaxies.

Findings

Detected radial metallicity gradients in the galaxies.

Fornax experienced extended star formation.

Sculptor, Ursa Minor, and Draco had brief, intense star formation episodes.

Abstract

We investigate the chemical abundance distributions of the Fornax, Sculptor, Ursa Minor, and Draco dwarf galaxies using Subaru/HSC photometric data. The HSC dataset, which includes broadband g and i filters and the narrowband NB515 filter, offers sensitivity to iron and magnesium abundances as well as surface gravity, enabling the identification of giant stars and foreground dwarfs. For analysis, we selected a total of 6713 giant candidates using a Random Forest regressor trained on medium-resolution (R ~ 6000) Keck/DEIMOS spectroscopic data. Our analysis reveals the extent of radial metallicity gradients in the galaxies. Such trends, not detectable in earlier studies, are now captured owing to the substantially enlarged sample size and areal coverage provided by the HSC data. These results are also consistent with chemical abundance patterns previously observed in the central regions through spectroscopic studies. Furthermore, we infer that Fornax underwent extended star formation, whereas Sculptor formed both metal-poor and metal-rich stars over a shorter time. Ursa Minor and Draco appear to have experienced brief, intense star formation episodes leading to nearly extinguished star formation. This study underscores the critical role of the expanded HSC dataset in revealing chemical gradients that were previously inaccessible. Future work incorporating additional spectra of metal-poor stars and age-sensitive isochrone modeling will enable more accurate maps of chemical abundance distributions.