Implications of a non-universal IMF from C, N, and O abundances in very metal-poor Galactic stars and damped Lyman-alpha absorbers

TL;DR

This study compares C, N, and O abundances in very metal-poor galactic stars and damped Lyman-alpha absorbers, suggesting a non-universal initial mass function with a cut-off at 20-25 solar masses in early Universe systems.

Contribution

It proposes that the observed abundance patterns indicate a truncated initial mass function in metal-poor DLA systems, providing new insights into early nucleosynthesis and galaxy evolution.

Findings

High C/O and low N/O ratios in DLA systems challenge existing models.

A cut-off in the initial mass function at 20-25 Msun explains abundance patterns.

Supports high N production in very massive stars with rapid rotation.

Abstract

Recently revealed C, N, and O abundances in the most metal-poor damped Lyman-alpha (DLA) absorbers are compared with those of extremely metal-poor stars in the Galactic halo, as well as extragalactic H II regions, to decipher nucleosynthesis and chemical enrichment in the early Universe. These comparisons surprisingly identify a relatively high C/O ratio and a low N/O ratio in DLA systems, which is hard to explain theoretically. We propose that if these features are confirmed by future studies, this effect occurs because the initial mass function in metal-poor DLA systems has a cut-off at the upper mass end at around 20-25 Msun, thus lacks the massive stars that provide the nucleosynthesis products leading to the low C/O and high N/O ratios. This finding is a reasonable explanation of the nature of DLA systems in which a sufficient amount of cold H I gas remains intact because of the suppression of ionization by massive stars. In addition, our claim strongly supports a high production rate of N in very massive stars, which might be acceptable in light of the recent nucleosynthesis calculations with fast rotation models. The updates of both abundance data and nucleosynthesis results will strengthen our novel proposition that the C/O and N/O abundances are a powerful tool for inferring the form of the initial mass function.