Modeling the Extragalactic Background Light from Stars and Dust
  The extragalactic background light (EBL) from the far infrared through the
visible and extending into the ultraviolet is thought to be dominated by
starlight, either through direct emission or through absorption and reradiation
by dust. This is the most important energy range for absorbing $\g$-rays from
distant sources such as blazars and gamma-ray bursts and producing electron
positron pairs. In previous work we presented EBL models in the optical through
ultraviolet by consistently taking into account the star formation rate (SFR),
initial mass function (IMF) and dust extinction, and treating stars on the main
sequence as blackbodies. This technique is extended to include post-main
sequence stars and reprocessing of starlight by dust. In our simple model, the
total energy absorbed by dust is assumed to be re-emitted as three blackbodies
in the infrared, one at 40 K representing warm, large dust grains, one at 70 K
representing hot, small dust grains, and one at 450 K representing polycyclic
aromatic hydrocarbons. We find our best fit model combining the Hopkins and
Beacom SFR using the Cole et al. parameterization with the Baldry and
Glazebrook IMF agrees with available luminosity density data at a variety of
redshifts. Our resulting EBL energy density is quite close to the lower limits
from galaxy counts and in some cases below the lower limits, and agrees fairly
well with other recent EBL models shortward of about 5 $\mu$m. Deabsorbing TeV
$\g$-ray spectra of various blazars with our EBL model gives results consistent
with simple shock acceleration theory. We also find that the universe should be
optically thin to $\g$-rays with energies less than 20 GeV.
