The energy distribution of the first supernovae

TL;DR

This study models the energy distribution of the first supernovae, accounting for unknown initial mass functions and stellar mixing, providing new constraints on Pop III star properties within a cosmological framework.

Contribution

It introduces the first constraints on the energy distribution function of Pop III supernovae, considering multiple unknowns simultaneously in a cosmological model.

Findings

Constraints on the energy distribution function exponent, 1 ≤ α_e ≤ 2.5.

Pop III IMF characteristic mass likely below 100 solar masses.

High probability that certain metal-poor stars were enriched by Pop III supernovae.

Abstract

The nature of the first Pop III stars is still a mystery and the energy distribution of the first supernovae is completely unexplored. For the first time we account simultaneously for the unknown initial mass function (IMF), stellar mixing, and energy distribution function (EDF) of Pop III stars in the context of a cosmological model for the formation of a MW-analogue. Our data-calibrated semi-analytic model is based on a N-body simulation and follows the formation and evolution of both Pop III and Pop II/I stars in their proper timescales. We discover degeneracies between the adopted Pop III unknowns, in the predicted metallicity and carbonicity distribution functions and the fraction of C-enhanced stars. Nonetheless, we are able to provide the first available constraints on the EDF, $dN/dE_\star \propto E_{\star}^{-\alpha_e}$ with $1\leq \alpha_e \leq2.5$. In addition, the characteristic mass of the Pop III IMF should be $m_{\rm ch}<100\:{\rm M_\odot}$, assuming a mass range consistent with hydrodynamical simulations (0.1-1000$\:{\rm M_\odot}$). Independent of the assumed Pop III properties, we find that all [C/Fe]>+0.7 stars (with [Fe/H]<-2.8) have been enriched by Pop III supernovae at a $>20\%$ level, and all [C/Fe]>+2 stars at a $>95\%$ level. All very metal-poor stars with $\rm [C/Fe]<0$ are predicted to be predominantly enriched by Pop III hypernovae and/or pair instabillity supernovae. To better constrain the primordial EDF, it is absolutely crucial to have a complete and accurate determination of the metallicity distribution function, and the properties of C-enhanced metal-poor stars (frequency and [C/Fe]) in the Galactic halo.