Horizon-AGN virtual observatory - 1. SED-fitting performance and
  forecasts for future imaging surveys
  Using the ligthcone from the cosmological hydrodynamical simulation
Horizon-AGN, we produced a photometric catalogue over $0<z<4$ with apparent
magnitudes in COSMOS, DES, LSST-like, and Euclid-like filters at depths
comparable to these surveys. The virtual photometry accounts for the complex
star formation history and metal enrichment of Horizon-AGN galaxies, and
consistently includes magnitude errors, dust attenuation and absorption by
inter-galactic medium. The COSMOS-like photometry is fitted in the same
configuration as the COSMOS2015 catalogue. We then quantify random and
systematic errors of photometric redshifts, stellar masses, and star-formation
rates (SFR). Photometric redshifts and redshift errors capture the same
dependencies on magnitude and redshift as found in COSMOS2015, excluding the
impact of source extraction. COSMOS-like stellar masses are well recovered with
a dispersion typically lower than 0.1 dex. The simple star formation histories
and metallicities of the templates induce a systematic underestimation of
stellar masses at $z<1.5$ by at most 0.12 dex. SFR estimates exhibit a
dust-induced bimodality combined with a larger scatter (typically between 0.2
and 0.6 dex). We also use our mock catalogue to predict photometric redshifts
and stellar masses in future imaging surveys. We stress that adding Euclid
near-infrared photometry to the LSST-like baseline improves redshift accuracy
especially at the faint end and decreases the outlier fraction by a factor
$\sim$2. It also considerably improves stellar masses, reducing the scatter up
to a factor 3. It would therefore be mutually beneficial for LSST and Euclid to
work in synergy.
