The cosmic spectral energy distribution in the EAGLE simulation
  The cosmic spectral energy distribution (CSED) is the total emissivity as a
function of wavelength of galaxies in a given cosmic volume. We compare the
observed CSED from the UV to the submm to that computed from the EAGLE
cosmological hydrodynamical simulation, post-processed with stellar population
synthesis models and including dust radiative transfer using the SKIRT code.
The agreement with the data is better than 0.15 dex over the entire wavelength
range at redshift $z=0$, except at UV wavelengths where the EAGLE model
overestimates the observed CSED by up to a factor 2. Global properties of the
CSED as inferred from CIGALE fits, such as the stellar mass density, mean star
formation density, and mean dust-to-stellar-mass ratio, agree to within better
than 20 per cent. At higher redshift, EAGLE increasingly underestimates the
CSED at optical-NIR wavelengths with the FIR/submm emissivity underestimated by
more than a factor of 5 by redshift $z=1$. We believe that these differences
are due to a combination of incompleteness of the EAGLE-SKIRT database, the
small simulation volume and the consequent lack of luminous galaxies, and our
lack of knowledge on the evolution of the characteristics of the interstellar
dust in galaxies. The impressive agreement between the simulated and observed
CSED at lower $z$ confirms that the combination of EAGLE and SKIRT dust
processing yields a fairly realistic representation of the local Universe.
