Finding He II: Testing Novel Models of Binary Populations across Cosmic Time

TL;DR

This paper compares different binary star evolution models to explain strong He II emission in high-redshift galaxies, aiming to improve understanding of massive star properties across cosmic time.

Contribution

It presents the first comparative analysis of binary evolution models, including BPASS and novel stripped star models, against high-z galaxy spectra.

Findings

Binary models better reproduce observed He II emission.

Different treatments of binaries significantly affect spectral predictions.

Insights into massive star evolution at high redshift are gained.

Abstract

Our understanding of massive stars remains incomplete. Many high-z galaxies and nearby analogs exhibit strong He II emission, indicating an abundance of photons with energies >54.4 eV that standard single-star population models cannot explain. Recent studies show that binary evolution and non-solar abundance patterns are required to explain the distinct spectra of high-z galaxies observed by JWST. However, treatments of these properties vary drastically between models. We present the first results from a comparison of models with different treatments of binaries, including BPASS and novel stripped star models, with rest-UV-optical spectra of high-z galaxies' local analogs. This type of investigation can provide insights into which aspects of binary evolution are important to reproduce observations and identify priorities in ongoing efforts to improve models. By constraining the properties of massive stars at high redshift, we can learn about the processes at play in high-z galaxies and massive star evolution more broadly.