Probing Chemical Enrichment in Extremely Metal-Poor Galaxies

The chemical composition of galaxies offers vital insights into their formation and evolution. A key aspect of this study is the correlation between helium abundance (He/H) and metallicity, which is instrumental in estimating the primordial helium produced during Big Bang nucleosynthesis. We investigate the chemical enrichment history of low-metallicity galaxies, with a particular focus on extremely metal-poor galaxies (EMPGs), using one-zone models. Our one-zone model, employing the Limongi & Chieffi (2018) yield, aligns well with observed high He/H ratios at low metallicities and successfully reproduces Fe/O ratios similar to those found in EMPGs. In contrast, the Nomoto et al. (2013) yield does not fully match the high Fe/O ratios observed in EMPGs. Furthermore, we explored models incorporating supermassive stars (SMS) as Pop III stars and intermittent star formation, both of which produced higher He/H ratios than the standard one-zone model. A model calculation that incorporates SMS yields effectively explain young galaxies (< $10^8$ years) with metallicities $(\mathrm{O/H}) \times 10^5 < 20$ and $\mathrm{He/H} > 0.085$. Notably, the model, where the outer envelope of the SMS's CO core is completely ejected, achieves $\mathrm{He/H} > 0.12$, aligning with the properties of high-$z$ galaxies recently discovered by JWST. Additionally, these models predict high N/O, consistent with JWST observations in the early universe.