  The Active Galactic Nuclei In Cosmological Simulations (AGNICS) project
includes AGN into the GalICS hybrid (N-body + semi-analytic) model to explore
the quasar-galaxy link in a cosmological perspective. The key problems are the
quasar fuelling mechanism, the origin of the BH to bulge mass relation, the
causal and chronological link between BH growth and galaxy formation, the
properties of quasar hosts and the role of AGN feedback in galaxy formation.
This first paper has two goals: to describe the general structure and the
assumptions of the method, and to apply AGNICS to studying the joint formation
of BHs and spheroids in galaxy mergers. We investigate under what conditions
this scenario can reproduce the local BH distribution and the evolution of the
quasar population. AGNICS contains two star formation modes: a quiescent one in
discs and a starburst one in protospheroids, the latter triggered by mergers
and disc instabilities. We assume that BH growth is linked to the starburst
mode. The simplest version of this scenario, in which the BH accretion rate and
the star formation rate in the starburst component are simply related by a
constant of proportionality, does not to reproduce the cosmic evolution of the
quasar population. A model in which this relation is modulated by a scaling
with the square root of the starburst gas density can explain the evolution of
the quasar luminosity function in B-band and X-rays (accounting for the
obscuration inferred from X-ray studies). The scatter and the tilt that this
model introduces in the BH-to-bulge mass relation are within the observational
constraints. The quasar contribution grows with bolometric luminosity and for a
given bulge mass the most massive BHs are in the bulges with the oldest stars.
