The most metal-poor, high redshift damped Lyman α systems (DLAs) provide a window to study some of the first few generations of stars. In this paper, we present a novel model to investigate the chemical enrichment of the near-pristine DLA population. This model accounts for the mass distribution of the enriching stellar population, the typical explosion energy of their supernovae, and the average number of stars that contribute to the enrichment of these DLAs. We conduct a maximum likelihood analysis of these model parameters using the observed relative element abundances ([C/O], [Si/O], and [Fe/O]) of the 11 most metal-poor DLAs currently known. We find that the mass distribution of the stars that have enriched this sample of metal-poor DLAs can be well-described by a Salpeter-like IMF slope at M > 10 M and that a typical metal-poor DLA has been enriched by 72 massive stars (95 per cent confidence), with masses 40 M . The inferred typical explosion energy (Ê exp = 1.8 +0.3 −0.2 × 10 51 erg) is somewhat lower than that found by recent works that model the enrichment of metal-poor halo stars. These constraints suggest that some of the metal-poor DLAs in our sample may have been enriched by Population II stars. Using our enrichment model, we also infer some of the typical physical properties of the most metal-poor DLAs. We estimate that the total stellar mass content is log 10 (M /M ) = 3.5 +0.3 −0.4 and the total gas mass is log 10 (M gas / M ) = 7.0 +0.3 −0.4 for systems with a relative oxygen abundance [O/H] ≈ −3.0.

Using science verification observations obtained with ESPRESSO at the Very Large Telescope (VLT) in 4UT mode, we report the first bound on the carbon isotope ratio 12 C/ 13 C of a quiescent, near-pristine damped Lyα (DLA) system at z = 2.34. We recover a limit log 10 12 C/ 13 C > +0.37 (2σ). We use the abundance pattern of this DLA, combined with a stochastic chemical enrichment model, to infer the properties of the enriching stars, finding the total gas mass of this system to be log 10 (M gas /M ) = 6.3 +1.4 −0.9 and the total stellar mass to be log 10 (M /M ) = 4.8±1.3. The current observations disfavour enrichment by metal-poor Asymptotic Giant Branch (AGB) stars with masses < 2.4 M , limiting the epoch at which this DLA formed most of its enriching stars. Our modelling suggests that this DLA formed very few stars until 1 Gyr after the cosmic reionization of hydrogen and, despite its very low metallicity (∼ 1/1000 of solar), this DLA appears to have formed most of its stars in the past few hundred Myr. Combining the inferred star formation history with evidence that some of the most metal-poor DLAs display an elevated [C/O] ratio at redshift z 3, we suggest that very metal-poor DLAs may have been affected by reionization quenching. Finally, given the simplicity and quiescence of the absorption features associated with the DLA studied here, we use these ESPRESSO data to place a bound on the possible variability of the fine-structure constant, ∆α/α = (−1.2 ± 1.1) × 10 −5 .

We investigate the intrinsic scatter in the chemical abundances of a sample of metal-poor ([Fe/H] &lt;−2.5) Milky Way halo stars. We draw our sample from four historic surveys and focus our attention on the stellar Mg, Ca, Ni, and Fe abundances. Using these elements, we investigate the chemical enrichment of these metal-poor stars using a model of stochastic chemical enrichment. Assuming that these stars have been enriched by the first generation of massive metal-free stars, we consider the mass distribution of the enriching population alongside the stellar mixing and explosion energy of their supernovae. For our choice of stellar yields, our model suggests that the most metal-poor stars were enriched, on average, by $\hat{N}_{\star }=5^{+13}_{-3}~(1\sigma )$ Population III stars. This is comparable to the number of enriching stars inferred for the most metal-poor DLAs. Our analysis therefore suggests that some of the lowest mass structures at z ∼ 3 contain the chemical products from &lt;13 (2σ) Population III enriched minihaloes. The inferred IMF is consistent with that of a Salpeter distribution and there is a preference towards ejecta from minimally mixed hypernovae. However, the estimated enrichment model is sensitive to small changes in the stellar sample. An offset of ∼0.1 dex in the [Mg/Ca] abundance is shown to be sensitive to the inferred number of enriching stars. We suggest that this method has the potential to constrain the multiplicity of the first generation of stars, but this will require: (1) a stellar sample whose systematic errors are well understood; and, (2) documented uncertainties associated with nucleosynthetic yields.

Some models of quantum gravity predict that the very structure of space–time is ‘frothy’ due to quantum fluctuations. Although the effect is expected to be tiny, if these space–time fluctuations grow over a large distance, the initial state of a photon, such as its energy, is gradually washed out as the photon propagates. Thus, in these models, even the most monochromatic light source would gradually disperse in energy due to space–time fluctuations over large distances. In this paper, we use science verification observations obtained with ESPRESSO at the Very Large Telescope to place a novel bound on the growth of space–time fluctuations. To achieve this, we directly measure the width of a narrow Fe ii absorption line produced by a quiescent gas cloud at redshift $z$ ≃ 2.34, corresponding to a comoving distance of ≃5.8 Gpc. Using a heuristic model where the energy fluctuations grow as σE/E = (E/EP)α, where EP ≃ 1.22 × 1028 eV is the Planck energy, we rule out models with α ≤ 0.634, including models where the quantum fluctuations grow as a random walk process (α = 0.5). Finally, we present a new formalism where the uncertainty accrued at discrete space–time steps is drawn from a continuous distribution. We conclude, if photons take discrete steps through space–time and accumulate Planck-scale uncertainties at each step, then our ESPRESSO observations require that the step size must be at least ≳ 1013.2lP, where lP is the Planck length.

We present precise abundance determinations of two near-pristine damped Lyα systems (DLAs) to assess the nature of the [O/Fe] ratio at [Fe/H] < −3.0 (i.e., <1/1000 of the solar metallicity). Prior observations indicate that the [O/Fe] ratio is consistent with a constant value, [O/Fe] ≃ +0.4, when −3 < [Fe/H] < −2, but this ratio may increase when [Fe/H] ≲ −3. In this paper, we test this picture by reporting new, high-precision [O/Fe] abundances in two of the most metal-poor DLAs currently known. We derive values of [O/Fe] = +0.50 ± 0.10 and [O/Fe] = +0.62 ± 0.05 for these two z ≃ 3 near-pristine gas clouds. These results strengthen the idea that the [O/Fe] abundances of the most metal-poor DLAs are elevated compared to DLAs with [Fe/H] ≳ −3. We compare the observed abundance pattern of the latter system to the nucleosynthetic yields of Population III supernovae (SNe), and find that the enrichment can be described by a (19–25) M⊙ Population III SN that underwent a (0.9–2.4) × 1051 erg explosion. These high-precision measurements showcase the behavior of [O/Fe] in the most metal-poor environments. Future high-precision measurements in new systems will contribute to a firm detection of the relationship between [O/Fe] and [Fe/H]. These data will reveal whether we are witnessing a chemical signature of enrichment from Population III stars and allow us to rule out contamination from Population II stars.