Simulating the infrared sky with a Spritz
  Current hydrodynamical and semi-empirical simulations of galaxy formation and
evolution have difficulties in reproducing the number densities of IR-detected
galaxies. Therefore, a versatile, phenomenological new simulation tool is
necessary to reproduce current and predict future observations at IR
wavelengths. In this work we generate simulated catalogues starting from the
Herschel infrared luminosity functions of different galaxy populations, in
order to consider in a consistent way different populations of galaxies and
active galactic nuclei. We associated a spectral energy distribution and
physical properties, such as stellar mass, star-formation-rate and AGN
contribution, to each simulated galaxy using a broad set of empirical
relations. We compare the resulting simulated galaxies, extracted up to z$=$10,
with a broad set of observational relations. The Spectro-Photometric
Realisations of Infrared-selected Targets at all-z (SPRITZ) simulation will
allow us to obtain in a fully consistent way simulated observations for a broad
set of current and future facilities with photometric capabilities as well as
low-resolution IR spectroscopy, like the James Webb Space Telescope (JWST) or
the Origin Space Telescope (OST). The derived simulated catalogue contains
galaxies and active galactic nuclei that by construction reproduce the observed
IR galaxy number density, but it is also in agreement with the observed number
counts from UV to far-IR wavelengths, the observed stellar mass function, the
star-formation-rate vs. stellar mass plane and the luminosity function from the
radio to the X-ray. The proposed simulation is therefore ideal to make
predictions for current and future facilities, in particular, but not limited
to, those operating at IR wavelengths. The SPRITZ simulation will be publicly
available.
