Extremely metal-poor stars in classical dwarf spheroidal galaxies: Fornax, Sculptor and Sextans

TL;DR

This study identifies and analyzes extremely metal-poor stars in the dwarf spheroidal galaxies Fornax, Sculptor, and Sextans, revealing their chemical compositions and implications for galaxy formation.

Contribution

First detection of extremely metal-poor stars in Fornax and Sextans, expanding understanding of metal-poor stellar populations in classical dwarf galaxies.

Findings

Fornax and Sextans contain extremely metal-poor stars, joining Sculptor.

The most metal-poor star observed in an external galaxy has [Fe/H]=-3.96.

Chemical abundance patterns provide insights into early galaxy formation and nucleosynthesis.

Abstract

We present the results of a dedicated search for extremely metal-poor stars in the Fornax, Sculptor and Sextans dSphs. Five stars were selected from two earlier VLT/Giraffe and HET/HRS surveys and subsequently followed up at high spectroscopic resolution with VLT/UVES. All of them turned out to have [Fe/H] <= -3 and three stars are below [Fe/H] -3.5. This constitutes the first evidence that the classical dSphs Fornax and Sextans join Sculptor in containing extremely metal-poor stars and suggests that all of the classical dSphs contain extremely metal-poor stars. One giant in Sculptor at [Fe/H]=-3.96 +- 0.10 is the most metal-poor star ever observed in an external galaxy. We carried out a detailed analysis of the chemical abundances of the alpha, iron peak, and the heavy elements, and we performed a comparison with the Milky Way halo and the ultra faint dwarf stellar populations. Carbon, barium and strontium show distinct features characterized by the early stages of galaxy formation and can constrain the origin of their nucleosynthesis.