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

We present new Keck/HIRES data of the most metal-poor damped Ly α (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 (2σ). We also provide the first upper limit on the relative abundance of an odd-atomic number element for this system [Al/H] < -3.82 (2σ). Our analysis thus confirms that this zabs ≃ 3.08 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 Boötes 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 zabs ≃ 3.08 (i.e. ∼2 Gyr after the Big Bang) may reside in one of the least polluted environments in the early Universe.