Spectral Signatures of Population III and Envelope-stripped Stars in Galaxies at the Epoch of Reionization

TL;DR

This study compares the spectral energy distributions of early-universe galaxies with different stellar populations, revealing that stripped stars and Population III stars significantly influence ionizing radiation outputs, especially in low-luminosity galaxies.

Contribution

It introduces a comparative analysis of SEDs from galaxies with single stars, stripped stars, and Population III stars, highlighting the impact of binary evolution products on reionization-era galaxy emissions.

Findings

Stripped stars lower the LyC power-law index in galaxy SEDs.

Galaxies with stripped stars show reduced FUV to LyC luminosity ratios.

SEDs of galaxies with stripped stars are distinct from those with Population III stars across all IMFs.

Abstract

While most simulations of the epoch of reionization have focused on single-stellar populations in star-forming dwarf galaxies, products of binary evolution are expected to significantly contribute to emissions of hydrogen-ionizing photons. Among these products are stripped stars (or helium stars), which have their envelopes stripped from interactions with binary companions, leaving an exposed helium core. Previous work has suggested these stripped stars can dominate the LyC photon output of high-redshift low luminosity galaxies. Other sources of hard radiation in the early universe include zero-metallicity Population III stars, which may have similar SED properties to galaxies with radiation dominated by stripped star emissions. Here, we use two metrics (the power-law exponent over wavelength intervals 240-500 \r{A}, 600-900 \r{A}, and 1200-2000 \r{A}, and the ratio of total luminosity in FUV wavelengths to LyC wavelengths) to compare the SEDs of simulated galaxies with only single-stellar evolution, galaxies containing stripped stars, and galaxies containing Population III stars, with four different IMFs. We find that stripped stars significantly alter the SEDs in the LyC range of galaxies at the epoch of reionization. SEDs in galaxies with stripped stars present have lower power-law indices in the LyC range and lower FUV to LyC luminosity ratios. These differences in SEDs are present at all considered luminosities ($M_{UV} > -15$, AB system), and are most pronounced for lower luminosity galaxies. We also find that SEDs of galaxies with stripped stars and Pop III stars are distinct from each other for all tested IMFs.