2009A&A...501..505L

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. 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 z_d=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. We obtain morphological merger fractions (f_m^mph) below 0.06 up to z ∼1. Parameterizing the merger fraction evolution with redshift as f_m^mph(z)=f_m^mph(0)(1+z)^m, we find that m=1.8±0.5 for M_B≤-20 galaxies, while m=5.4±0.4 for M_*≥10¹⁰M_☉ galaxies. When we translate our merger fractions to merger rates (R_m^mph), their evolution, parameterized as R_m^mph(z)=R_m^mph(0)(1+z)ⁿ, is quite similar in both cases: n=3.3±0.8 for M_B≤-20 galaxies, and n=3.5±0.4 for M_*≥10¹⁰M_☉ galaxies. 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.