THE MINOR ROLE OF GAS-RICH MAJOR MERGERS IN THE RISE OF INTERMEDIATE-MASS EARLY TYPES AT z ≤ 1

We study the evolution of galaxy structure since z similar to 1 to the present. From a Great Observatories Origins Deep Survey South (GOODS-S) multi-band catalog, we define (blue) luminosity-and mass-weighted samples, limited by M-B <= -20 and M-star >= 10(10) M-circle dot, comprising 1122 and 987 galaxies, respectively. We extract early-type (ET; E/S0/Sa) and late-type (LT; Sb-Irr) subsamples by their position in the concentration-asymmetry plane, in which galaxies exhibit a clear bimodality. We find that the ET fraction, f(ET), rises with cosmic time, with a corresponding decrease in the LT fraction, f(LT), in both luminosity-and mass-selected samples. However, the evolution of the comoving number density is very different: the decrease in the total number density of M-B <= -20 galaxies since z = 1 is due to the decrease in the LT population, which accounts for similar to 75% of the total star formation rate in the range under study, while the increase in the total number density of M-star >= 10(10) M-circle dot galaxies in the same redshift range is due to the evolution of ETs. This suggests that we need a structural transformation between LT galaxies that form stars actively and ET galaxies in which the stellar mass is located. Comparing the observed evolution with the gas-rich major merger rate in GOODS-S, we infer that only similar to 20% of the new ET galaxies with M-star >= 10(10) M-circle dot appeared since z similar to 1 can be explained by this kind of mergers, suggesting that minor mergers and secular processes may be the driving mechanisms of the structural evolution of intermediate-mass (M-star similar to 4 x 10(10) M-circle dot) galaxies since z similar to 1.