Linking dwarf galaxies to halo building blocks with the most metal-poor star in Sculptor

TL;DR

This study confirms that the most metal-poor star in the Sculptor dwarf galaxy shares chemical characteristics with ancient halo stars, supporting the idea that early galaxy building blocks were similar to current dwarf galaxies.

Contribution

It provides high-resolution spectroscopic evidence linking a dwarf galaxy star to the early stellar halo, challenging previous assumptions about their differences.

Findings

The star's iron abundance is less than 1/4000th of the Sun.

The chemical pattern matches that of low-metallicity halo stars.

Dwarf galaxy progenitors and halo stars likely had similar chemical enrichment.

Abstract

Current cosmological models indicate that the Milky Way's stellar halo was assembled from many smaller systems. Based on the apparent absence of the most metal-poor stars in present-day dwarf galaxies, recent studies claimed that the true Galactic building blocks must have been vastly different from the surviving dwarfs. The discovery of an extremely iron-poor star (S1020549) in the Sculptor dwarf galaxy based on a medium-resolution spectrum cast some doubt on this conclusion. However, verification of the iron-deficiency and measurements of additional elements, such as the alpha-element Mg, are mandatory for demonstrating that the same type of stars produced the metals found in dwarf galaxies and the Galactic halo. Only then can dwarf galaxy stars be conclusively linked to early stellar halo assembly. Here we report high-resolution spectroscopic abundances for 11 elements in S1020549, confirming the iron abundance of less than 1/4000th that of the Sun, and showing that the overall abundance pattern mirrors that seen in low-metallicity halo stars, including the alpha-elements. Such chemical similarity indicates that the systems destroyed to form the halo billions of years ago were not fundamentally different from the progenitors of present-day dwarfs, and suggests that the early chemical enrichment of all galaxies may be nearly identical.