Evolution of the frequency of luminous (≥L* _v) close galaxy pairs at z < 1.2 in the COSMOS field

We measure the fraction of luminous galaxies in pairs at projected separations of 5-20 kpc out to z = 1.2 in the Cosmic Evolution Survey (COSMOS) field using ACS images and photometric redshifts derived from an extensive multiwavelength data set. Analysis of a complete sample of 106,188 galaxies more luminous than My = -1.9.8 (∼L* _V) in the redshift range 0.1 < z < 1.2 yields 1749 galaxy pairs. These data are supplemented by a local (z = 0-0.1)value for the galaxy pair fraction derived from the Sloan Digital Sky Survey. After statistically correcting the COSMOS pair sample for chance line-of-sight superpositions, the evolution in the pair fraction is fit by a power law ∝(1 + z) ^n=3.1*0.1. If this strongly evolving pair fraction continues out to higher redshift, ∼50% of all luminous galaxies at z ∼ 2 are in close pairs. This clearly signifies that galaxy mergers are a very significant and possibly dominant mechanism for galaxy evolution during the epoch of galaxy formation at z = 1-3.