Constraining the near-IR background light from Population-III stars
  using high redshift gamma-ray sources
  The Fermi satellite has detected GeV emission from a number of gamma-ray
bursts and active galactic nuclei at high redshift, z > 1.5. We examine the
constraints that the detections of gamma rays from several of these sources
place on the contribution of population-III stars to the extragalactic
background light. Emission from these primordial stars, particularly redshifted
Lyman-alpha emission, can interact with gamma rays to produce electron-positron
pairs and create an optical depth to the propagation of gamma-ray emission, and
the detection of emission above 10 GeV can therefore constrain the production
of this background. We consider two initial mass functions for the early stars,
and use derived SEDs for each to put upper limits on the star-formation rate
density of massive early stars from redshifts 6 to 10. Our limits are
complementary to those set on a high near-IR background flux by ground-based
TeV-scale observations, and show that current data can limit star-formation in
the late stages of reionization to less than 0.5 M_solar yr^-1 Mpc^-3. Our
results also show that the total background flux from population-III stars must
be considerably less than that from resolved galaxies at wavelengths below 1.5
microns.
