  It is well-known that feedback processes play a fundamental role in the
regulation of star formation (SF) and, in particular, in the quenching of
early-type galaxies (ETGs) as have been inferred by numerical studies of
LambdaCDM universe models. At the same time, ETGs are subject to certain
fundamental scaling relations, but the connection between them and the physical
processes that effect ETG evolution remain unknown. This work aims at studying
the impact of the energetic feedback due to active galactic nuclei (AGN) in the
formation and evolution of ETGs. Especially, we assess to what extent modelling
AGN feedback is necessary to reproduce observational constrains such as
morphology, kinematics and the evolution of the main scaling relations. The
Horizon-AGN and Horizon-noAGN cosmological hydrodynamical simulations were
performed with identical initial conditions and including the same physical
processes with the exception of the AGN feedback in the former. We select a
sample of ETGs from both simulations using the same criteria and subject them
to an exhaustive study regarding SF activity, kinematics and scaling relations.
We find that galaxies from Horizon-AGN follow observed fundamental scaling
relations (mass-plane, Fundamental Plane, mass-size relation) and reproduce,
qualitatively, kinematic features such as the bimodality in the spin parameter
distribution at z = 0. The specific star formation activity is within observed
ranges when AGN is turned on. Instead, galaxies formed in absence of AGN
feedback show differences with observations such as the departure from the
Fundamental Plane (FP) of a group of galaxies that have an excess of stellar
surface density, and a shallower mass-size relation populated by galaxies with
young stellar ages. Abridged
