  The z=8 galaxy sample (EGSY-2008532660, EGS-zs8-1, EGS-zs8-2), observed with
HST and Spitzer/IRAC, was selected for its atypical [3.6]-[4.5]mum IR excess.
The best-fitting of observations is processed with multiple libraries of
continuous UV-to-farIR spectral energy distributions (SEDs) with the help of
the code Pegase.3 with dust (Fioc and Rocca-Volmerange, 2018, submitted to AA).
The main results are: i) the IR excess is due to the Balmer break of red giant
stars with galaxy ages of 450-500 Myrs ii) masses are high: 7 10^10 Msun for
stellar mass, 10^11 Msun for galaxy mass, 3 10^8 Msun for dust mass iii) they
are probing mature (no starbursting) galaxies only with the simulations of
spheroidal (and no spiral) geometries and the star formation history (SFH ) of
massive ellipticals. Less constrained by observations not covering the Balmer
zone, the galaxy GN-z11 is consistent. These results constrain the rapid and
efficient formation of massive elliptical galaxies, significantly distinct of
early-type disk-spiral galaxies, and the reionization of the Universe
