Lyman and Balmer breaks reveal mature z=8 galaxies with the code Pegase.3.

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