The main sequence of star forming galaxies II. A non evolving slope at the high mass end.

By using the deepest available mid and far infrared surveys in the CANDELS, GOODS and COSMOS fields we study the evolution of the Main Sequence (MS) of star forming galaxies (SFGs) from z~0 to` ~2.5 at stellar masses larger than 10^{10} M_{\odot}. The MS slope and scatter are consistent with a re-scaled version of the local relation and distribution, shifted at higher values of SFR according to ~(1+z)^{3.2}. The relation exhibits a bending at the high mass end and a slightly increasing scatter as a function of the stellar mass. We show that the previously reported evolution of the MS slope, in the considered mass and redshift range, is due to a selection effect. The distribution of galaxies in the MS region at fixed stellar mass is well represented by a single log-normal distribution at all redshifts and masses, with starburst galaxies (SBs) occupying the tail at high SFR.