The most iron-deficient stars as the polluted population III stars

TL;DR

This study models how interstellar matter accretion can explain the extremely low metallicity of the most iron-deficient stars, suggesting they are Population III stars polluted by their environment.

Contribution

It introduces a chemical evolution model within hierarchical galaxy formation to explain the metallicity of the most iron-poor stars, linking ISM accretion to their observed properties.

Findings

The metallicity distribution matches observations of extremely metal-poor stars.

The lowest metallicity stars can be explained as Population III stars polluted by ISM.

ISM accretion accounts for the origin of iron group elements in stars with [Fe/H] < -5.

Abstract

We investigate the origin of the most iron-poor stars including SMSS J031300.36-670839.3 with [Fe/H] < -7.52. We compute the change of surface metallicity of stars with the accretion of interstellar matter (ISM) after their birth using the chemical evolution model within the framework of the hierarchical galaxy formation. The predicted metallicity distribution function agrees very well with that observed from extremely metal-poor stars. In particular, the lowest metallicity tail is well reproduced by the Population III stars whose surfaces are polluted with metals through ISM accretion. This suggests that the origin of iron group elements is explained by ISM accretion for the stars with [Fe/H]$\lesssim -5$. The present results give new insights into the nature of the most metal-poor stars and the search for Population III stars with pristine abundances.