The stochastic enrichment of Population II stars

Abstract

We investigate the intrinsic scatter in the chemical abundances of a sample of metal-poor ([Fe/H] <−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 <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.

Supernova-driven turbulent metal mixing in high redshift galactic disks: metallicity fluctuations in the interstellar medium and its imprints on metal poor stars in the Milky Way

“…Our results suggest that while it is unlikely, at the SFRs considered here, to form stars from gas that has been enriched by a single event, stars with enrichment by a few events are plausible at [Fe/H] −2. This is in broad agreement with the results of Welsh et al (2021) who modelled the stochastic enrichment of metal poor stars by the first SNe and found the expected number of enriching first SNe to the most metal poor stars to be N SNe = 5 +13 −3 . Our simulations suggest that the ISM in the galactic disk patches increased rapidly in metallicity after less than 100 Myr.…”

Supernova-driven Turbulent Metal Mixing in High-redshift Galactic Disks: Metallicity Fluctuations in the Interstellar Medium and its Imprints on Metal-poor Stars in the Milky Way

“…Our results suggest, that while it is unlikely (at the SFRs considered here) to form stars from gas that has been enriched by a single event, stars with enrichment by a few events are plausible at 〈[Fe/H]  − 2. This is in broad agreement with the results of Welsh et al (2021) who modeled the stochastic enrichment of metal-poor stars by the first SNe and found the expected number of enriching first SNe to the most metal-poor stars to be = -+ N 5 SNe 3 13 . Our simulations suggest that the ISM in the galactic disk patches increased rapidly in metallicity after less than 100 Myr.…”

Connecting Primordial Star-forming Regions and Second-generation Star Formation in the Phoenix Simulations

“…Although their extreme time resolution was intended to provide a high resolution of star formation and feedback events for training DNNs, the PHX suite also provides a unique opportunity to study the transition between Population III and second-generation (Population II.1) 3 star formation. Studying low-metallicity stars or damped Lyα systems in observations is currently our only window into the Population III initial mass function (IMF; Cooke et al 2017;Welsh et al 2019Welsh et al , 2020, but the uncertainty in the IMF (Nakamura & Umemura 2002;Ishigaki et al 2018) and metallicity of Population II.1 stars that could form from enriching events makes inferences about the Population III era difficult. Due to the fine time resolution in the PHX suite outputs, we use them to study the formation state of small Population II star clusters, as well as the evolution of Population III star-forming regions.…”