The galaxy major merger fraction to ~ 1

¹ Instituto de Astrofísica de Canarias, Calle Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain e-mail: clsj@iac.es
² Departamento de Astrofísica y Ciencias de la Atmósfera, Facultad de C.C. Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
³ European South Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany

Received: 23 February 2009
Accepted: 12 May 2009

Abstract

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 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.

Results. We obtain morphological merger fractions below 0.06 up to z ~ 1. Parameterizing the merger fraction evolution with redshift as , we find that m = 1.8 ± 0.5 for M_B ≤ -20 galaxies, while m = 5.4 ± 0.4 for ≥ 10¹⁰ galaxies. When we translate our merger fractions to merger rates , their evolution, parameterized as , is quite similar in both cases: n = 3.3 ± 0.8 for M_B ≤ -20 galaxies, and n = 3.5 ± 0.4 for ≥ 10¹⁰ galaxies.

Conclusions. Our results imply that only ~8% of today's ≥ 10¹⁰ galaxies have undergone a disc-disc major merger since z ~ 1. In addition, ~21% of 10¹⁰ 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 ≥ 10¹⁰ galaxies since z ~ 1, with only 0.2 disc-disc major mergers per galaxy, but may be an important process at , with merger per galaxy at 1 < z < 3.