The galaxy major merger fraction to z ~ 1

Aims. The importance of disc-disc major mergers in galaxy evolution remains uncertain. We study the major merger fraction in a SPITZER/IRAC-selected catalogue in the GOODS-S field up to z ~ 1 for luminosity- and mass-limited samples.Methods. We select disc-disc merger remnants on the basis of morphological asymmetries/distortions, and address three main sources of systematic errors: (i) we explicitly apply morphological K-corrections; (ii) we measure asymmetries in galaxies artificially redshifted to zd= 1.0 to deal with loss of morphological information with redshift; and (iii) we take into account the observational errors in z and A, which tend to overestimate the merger fraction, though use of maximum likelihood techniques.Results. We obtain morphological merger fractions (fmmph) below 0.06 up to z ~ 1. Parameterizing the merger fraction evolution with redshift as fmmph(z) = fmmph(0) (1+z)m, we find that m = 1.8 ? 0.5 for MB? -20 galaxies, while m = 5.4 ? 0.4 for M*? 1010M?galaxies. When we translate our merger fractions to merger rates (Remmph), their evolution, parameterized as Remmph(z) = Remmph(0) (1+z)n, is quite similar in both cases: n = 3.3 ? 0.8 for MB? -20 galaxies, and n = 3.5 ? 0.4 for M*? 1010M?galaxies.Conclusions. Our results imply that only ~8% of today's M*? 1010M?galaxies have undergone a disc-disc major merger since z ~ 1. In addition, ~21% of M*? 1010M?galaxies at z ~ 1 have undergone one of these mergers since z ~ 1.5. This suggests that disc-disc major mergers are not the dominant process in the evolution of M*? 1010M?galaxies since z ~ 1, with only 0.2 disc-disc major mergers per galaxy, but may be an important process at z > 1, with ?1 merger per galaxy at 1 < z < 3.