We compare the results from a semi-analytic model of galaxy formation with
spectro-photometric observations of distant galaxy clusters observed in the
range 0.8< z< 1.3. We investigate the properties of their red sequence (RS)
galaxies and compare them with those of the field at the same redshift. In our
model we find that i) a well-defined, narrow RS is obtained already by z= 1.2;
this is found to be more populated than the field RS, analogously to what
observed and predicted at z=0; ii) the predicted U-V rest-frame colors and
scatter of the cluster RS at z=1.2 have average values of 1 and 0.15
respectively, with a cluster-to-cluster variance of 0.2 and 0.06, respectively.
The scatter of the RS of cluster galaxies is around 5 times smaller than the
corresponding field value; iii) when the RS galaxies are considered, the mass
growth histories of field and cluster galaxies at z=1.2 are similar, with 90 %
of the stellar mass of RS galaxies at z=1.2 already formed at cosmic times
t=2.5 Gyr, and 50 % at t=1 Gyr; v) the predicted distribution of stellar ages
of RS galaxies at z=1.2 peaks at 3.7 Gyr for both cluster and field
populations; however, for the latter the distribution is significantly skewed
toward lower ages. When compared with observations, the above findings show an
overall consistency, although the average value 0.07 of the observed cluster RS
scatter (U-V colors) at z=1.2 is smaller than the corresponding model central
value. We discuss the physical origin and the significance of the above results
in the framework of cosmological galaxy formation.Comment: 14 pages, accepted for publication in ApJ. Updated one referenc