The Diversity of Metal-Enrichment and Abundance Patterns at High Redshift: A Magellan Survey of Gas-rich Galaxies Traced by Damped Lyman-alpha Absorbers at z~5

TL;DR

This study investigates the metal enrichment and abundance patterns in high-redshift damped Lyman-alpha absorbers, revealing diverse metallicities, evidence of early star contributions, and the presence of dust even at z~5.

Contribution

First comprehensive survey of element abundances in DLAs at z>4, showing diversity in metallicities and evidence of early stellar populations.

Findings

DLA metallicities at z>4.5 span ~3 orders of magnitude.

Metallicity dispersion increases at higher redshifts.

Evidence of Pop III star contributions in some DLAs.

Abstract

A powerful technique to trace the signatures of the first stars is through the metal enrichment in concentrated reservoirs of hydrogen, such as the damped Lyman-alpha absorbers (DLAs) in the early universe. We conducted a survey aimed at discovering DLAs along sight lines to high-z quasars in order to measure element abundances at z>4. Here we report our first results from this survey for 10 DLAs with redshifts of ~4.2-5.0. We determine abundances of C, O, Si, S, and Fe, and thereby the metallicities and dust depletions. We find that DLA metallicities at z>4.5 show a wide diversity spanning ~3 orders of magnitude. The metallicities of DLAs at 3.7<z<5.3 show a larger dispersion compared to that at lower redshifts. Combining our sample with the literature, we find a relatively smooth evolution of metallicity with redshift out to z~5.3, with a tentative (~2 sigma) indication of a slight rise in metallicity at 4.5<z<5.3. The relative abundances exhibit C enhancement for both metal-poor and metal-enriched DLAs. In addition, alpha-element enhancement is evident in some DLAs, including a DLA at z=4.7 with a super-solar metallicity. Comparing [C/O] and [Si/O] with model predictions, 4 DLAs in our survey seem consistent with a non-zero Pop III contribution (3 with >=30% Pop-III contribution). Combining our sample and the literature, we find the dust depletion strength and dust-to-metal ratios to correlate positively with the total (gas+solid phase) metallicity, confirming the presence of metal-rich, dusty DLAs even at ~1 billion years after the Big Bang.