The Chemical Evolution of Very Metal-Poor Damped Lyman-$\alpha$ Systems

TL;DR

This paper models the chemical evolution of very metal-poor damped Lyman-$\\alpha$ systems at $z\sim2$, comparing simulations to observations, and explores star formation and supernova enrichment scenarios to explain their metallicity and abundance patterns.

Contribution

It introduces two models for the chemical enrichment history of metal-poor DLAs, linking them to ultrafaint dwarf galaxies and supernova enrichment processes.

Findings

Simulations match observed gas densities but not metallicities with single supernova models.

A single burst star formation model explains DLA abundances but not [$\alpha$/Fe] suppression.

A two-burst model with Type Ia supernovae accounts for observed abundance patterns.

Abstract

In earlier work we showed that a dark matter halo with a virial mass of $10^7$ M$_\odot$ can survive feedback from its own massive stars and form stars for $\gtrsim100$ Myr. We also found that our modelled systems were consistent with observations of ultrafaint dwarfs (UFDs), the least massive known galaxies. Very metal-poor damped Lyman-$\alpha$ systems (DLAs) recently identified at $z\sim2$ may represent the gas that formed at least some of the observed stars in UFDs. We compare projected sightlines from our simulations to the observed metal-poor DLAs and find that our models can reach the densities of the observed sightlines; however the metallicities are inconsistent with the single supernova simulations, suggesting enrichment by multiple supernovae. We model two scenarios for the history of these systems. The first explains the gas abundances in DLAs by a single burst of star formation. This model can produce the observed DLA abundances, but does not provide an explanation as to why the DLAs show suppressed [$\alpha$/Fe] compared to the stellar population of UFDs. The second scenario splits the DLAs into a population which is enriched by a single burst, and a population that is enriched by a second burst after the accretion of metal-poor gas. In this scenario, the suppressed average [$\alpha$/Fe] in DLAs compared to UFDs results from enrichment of second-burst systems by Type Ia supernovae.