The explosion energy of early stellar populations: The Fe-peak element ratios in low metallicity damped Lyman-alpha systems

TL;DR

This study investigates Fe-peak element ratios in very metal-poor damped Lyman-alpha systems to infer the explosion energies of early supernovae, using new spectral stacking methods and comparing with stellar data.

Contribution

It introduces a novel spectral stacking technique to estimate Fe-peak ratios in low-metallicity DLAs and links these ratios to supernova explosion energies of early stars.

Findings

Most DLAs were enriched by supernovae with energies less than 1.2 x 10^51 erg.

Spectral stacking effectively estimates element ratios in systems without direct detections.

Future observations with 30-m class telescopes could measure supernova energies of the first stars.

Abstract

The relative abundances of the Fe-peak elements (Ti-Zn) at the lowest metallicities are intimately linked to the physics of core-collapse supernova explosions. With a sample of 25 very metal-poor damped Lyman-alpha systems, we investigate the trends of the Fe-peak element ratios with metallicity. For nine of the 25 DLAs, a direct measurement (or useful upper limit) of one or more of the Ti,Cr,Co,Ni,Zn/Fe abundance ratios could be determined from detected absorption lines. For the remaining systems (without detections), we devised a new form of spectral stacking to estimate the typical Fe-peak element ratios of the DLA population in this metallicity regime. We compare these data to analogous measurements in metal-poor stars of the Galactic halo and to detailed calculations of explosive nucleosynthesis in metal-free stars. We conclude that most of the DLAs in our sample were enriched by stars that released an energy of < 1.2 x 10^51 erg when they exploded as core-collapse supernovae. Finally, we discuss the exciting prospect of measuring Fe-peak element ratios in damped Lyman-alpha systems with Fe/H < 1/1000 of solar when 30-m class telescopes become available. Only then will we be able to pin down the energy that was released by the supernovae of the first stars.