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