The high-redshift evolution of the Red Sequence scatter from joint
  simulations and HAWK-I Cluster Survey
  We study the evolution of the Red Sequence (RS) scatter in galaxy clusters
and groups simultaneously using predictions from our simulations (cosmological
hydrodynamic + semi-analytical) as well as observational data from the HAWK-I
Cluster Survey (HCS), a sample of galaxy clusters at redshifts $0.8 < z < 1.5$.
We analyze the intrinsic scatter of the RS to investigate whether the stellar
age can be its main effective driver, at the same time assessing the role of
metallicity variations in shaping the RS building at around epoch $z\sim$1 and
beyond. To this purpose we rely on various methods to derive the average age
and age spread from the RS colour scatter of the HCS sample, with the aid of
population synthesis models. The RS scatter predicted by the models at $z< 0.7$
is found to not depend on the star formation history adopted, whilst at $z>the
correlation found between age and rest-frame colour scatters is quite robust,
although all age scatter estimations ultimately depend on the definition of RS
as well as on the completeness limits adopted. We find that the age spread of
RS galaxies predicted by both hydrodynamical simulations and SAM increases with
cosmic epoch, while the ratio between the age spread and the average age
remains approximately constant. Both trends are in agreement with observational
results from both the HCS and other literature samples.
