  Unusual patterns of recombination emission from gas ionized by metal-free
stars may distinguish early star-forming galaxies from their present-day
counterparts. This pattern arises from the harder ionizing spectrum expected
from metal-free stars, which strongly enhances the strength of He II
recombination lines. Our calculations indicate that line fluxes of He II 1640
and 4686 are sufficiently large to be detected by narrowband and spectroscopic
searches for high-redshift emission-line sources at redshift z ~ 5 using
current instruments. An unknown fraction of Lya emitters may harbor
low-metallicity or metal-free stars. As the predicted He II 1640 flux is
comparable to and may exceed hydrogen Lya, searches for high-redshift galaxies
should consider He II recombination lines as possible identifications for
single emission lines in observed spectra. Spectra of metal-free stars may show
both H I and He II emission lines, improving the constraints on their redshift
and identification. We assess the considerable uncertainties that affect our
expectations for the detection and identification of true first-generation
stars with present search techniques, including the role of stellar mass loss
in spectral evolution and the confusion of ionization by primordial stellar
sources and AGN in the early universe.
