Extragalactic Background Light Inferred from AEGIS Galaxy SED-type
  Fractions
  The extragalactic background light (EBL) is of fundamental importance both
for understanding the entire process of galaxy evolution and for gamma-ray
astronomy, but the overall spectrum of the EBL between 0.1-1000 microns has
never been determined directly from galaxy spectral energy distribution (SED)
observations over a wide redshift range. The evolving, overall spectrum of the
EBL is derived here utilizing a novel method based on observations only. This
is achieved from the observed evolution of the rest-frame K-band galaxy
luminosity function up to redshift 4 (Cirasuolo et al. 2010), combined with a
determination of galaxy SED-type fractions. These are based on fitting SWIRE
templates to a multiwavelength sample of about 6000 galaxies in the redshift
range from 0.2 to 1 from the All-wavelength Extended Groth Strip International
Survey (AEGIS). The changing fractions of quiescent galaxies, star-forming
galaxies, starburst galaxies and AGN galaxies in that redshift range are
estimated, and two alternative extrapolations of SED-types to higher redshifts
are considered. This allows calculation of the evolution of the luminosity
densities from the UV to the IR, the evolving star formation rate density of
the universe, the evolving contribution to the bolometric EBL from the
different galaxy populations including AGN galaxies and the buildup of the EBL.
Our EBL calculations are compared with those from a semi-analytic model, from
another observationally-based model and observational data. The EBL
uncertainties in our modeling based directly on the data are quantified, and
their consequences for attenuation of very high energy gamma-rays due to pair
production on the EBL are discussed. It is concluded that the EBL is well
constrained from the UV to the mid-IR, but independent efforts from infrared
and gamma-ray astronomy are needed in order to reduce the uncertainties in the
far-IR.
