Can Population III stars be major origins of both merging binary black holes and extremely metal poor stars?

TL;DR

This study investigates whether Population III stars could be the main source of merging binary black holes and extremely metal-poor stars, finding constraints on their initial mass function and star formation efficiency.

Contribution

It provides new constraints on the initial mass function of Pop III stars and assesses their role in black hole mergers and EMP star formation.

Findings

Pop III star formation efficiency must be higher than theoretical predictions for observed BH merger rates.

EMP star abundance patterns restrict Pop III initial mass to 15-27 solar masses.

Pop III stars could still be the dominant origin of merging binary black holes.

Abstract

Population (Pop) III stars, first stars, or metal-free stars are made of primordial gas. We have examined if they can be dominant origins of merging binary black holes (BHs) and extremely metal-poor stars. The abundance pattern of EMP stars is helpful to trace back the properties of Pop III stars. We have confirmed previous arguments that the observed BH merger rate needs Pop III star formation efficiency 10 times larger than theoretically predicted values, while the cosmic reionization history still permits such a high Pop III star formation efficiency. On the other hand, we have newly found that the elemental abundance pattern of EMP stars only allows the Pop III initial mass function with the minimum mass of $\sim 15 - 27$ $M_\odot$. In other words, the minimum mass must not deviate largely from the critical mass below and above which Pop III stars leave behind neutron stars and BHs, respectively. Pop III stars may be still a dominant origin of merging binary BHs but our study has reduced the allowed parameter space under a hypothesis that EMP stars are formed from primordial gas mixed with Pop III supernova ejecta.