Evolution of the frequency of luminous (≥Lv*) 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 M-V =19.8 (similar to 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 alpha( 1+ z) (n) (=3.1 +/- 0.1). If this strongly evolving pair fraction continues out to higher redshift, similar to 50% of all luminous galaxies at z similar to 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.