Comparing Galaxy Clustering in Horizon-AGN Simulated Lightcone Mocks and
  VIDEO Observations
  Hydrodynamical cosmological simulations have recently made great advances in
reproducing galaxy mass assembly over cosmic time - as often quantified from
the comparison of their predicted stellar mass functions to observed stellar
mass functions from data. In this paper we compare the clustering of galaxies
from the hydrodynamical cosmological simulated lightcone Horizon-AGN, to
clustering measurements from the VIDEO survey observations. Using mocks built
from a VIDEO-like photometry, we first explore the bias introduced into
clustering measurements by using stellar masses and redshifts derived from
SED-fitting, rather than the intrinsic values. The propagation of redshift and
mass statistical and systematic uncertainties in the clustering measurements
causes us to underestimate the clustering amplitude. We find then that
clustering and halo occupation distribution (HOD) modelling results are
qualitatively similar in Horizon-AGN and VIDEO. However at low stellar masses
Horizon-AGN underestimates the observed clustering by up to a factor of ~3,
reflecting the known excess stellar mass to halo mass ratio for Horizon-AGN low
mass haloes, already discussed in previous works. This reinforces the need for
stronger regulation of star formation in low mass haloes in the simulation.
Finally, the comparison of the stellar mass to halo mass ratio in the simulated
catalogue, inferred from angular clustering, to that directly measured from the
simulation, validates HOD modelling of clustering as a probe of the galaxy-halo
connection.
