Towards ultra metal-poor DLAs: linking the chemistry of the most metal-poor DLA to the first stars

TL;DR

This study presents the most metal-poor DLA known, analyzes its chemical composition to infer its enrichment history, and compares it to ancient stars, suggesting a link to the first stars and early universe environments.

Contribution

It provides new ultra-metal-poor DLA data, improves abundance limits, and models its enrichment as originating from a single Population III star, offering insights into early cosmic chemical evolution.

Findings

Confirmed the DLA as the most iron-poor known.

Modeled enrichment as from a single Population III star.

Identified a similar star in Bootes I with comparable chemistry.

Abstract

We present new Keck/HIRES data of the most metal-poor damped Lyman-alpha (DLA) system currently known. By targeting the strongest accessible Fe II features, we have improved the upper limit of the [Fe/H] abundance determination by ~1 dex, finding [Fe/H]<-3.66 (2 sigma). We also provide the first upper limit on the relative abundance of an odd-atomic number element for this system [Al/H]<-3.82 (2 sigma). Our analysis thus confirms that this z_abs=3.07 DLA is not only the most metal-poor DLA but also the most iron-poor DLA currently known. We use the chemistry of this DLA, combined with a stochastic chemical enrichment model, to probe its enrichment history. We find that this DLA is best modelled by the yields of an individual Population III progenitor rather than multiple Population III stars. We then draw comparisons with other relic environments and, particularly, the stars within nearby ultra-faint dwarf galaxies. We identify a star within Bootes I, with a similar chemistry to that of the DLA presented here, suggesting that it may have been born in a gas cloud that had similar properties. The extremely metal-poor DLA at redshift z_abs=3.07 (i.e. ~2 Gyrs after the Big Bang) may reside in one of the least polluted environments in the early Universe.