Gamma-Ray Absorption By The Cosmic Lyman Continuum From Star-forming
  Galaxies
  Motivated by the discovery of the ultra-strong emission line starburst
galaxies (EELGs) known as "green pea galaxies", we consider here their
contribution to the intergalactic flux of ionizing UV at high redshifts. Most
galaxies that have been observed show a precipitous drop in their flux blueward
of the Lyman limit. However, recent observations of EELGs have discovered that
many more Lyman continuum photons escape from them into intergalactic space
than was previously suspected. We calculate their contribution to the
extragalactic background light (EBL). We also calculate the effect of these
photons on the absorption of high energy $\gamma$-rays. For the more distant
$\gamma$-ray sources, particularly at $z \ge 3$, the intergalactic opacity
above a few GeV is significantly higher than previous estimates which ignored
the Lyman continuum photons. We calculate the results of this increased opacity
on observed $\gamma$-ray spectra, which produces a high-energy turnover
starting at lower energies than previously thought, and a gradual spectral
steepening that may also be observable.
