  We measure the fraction of luminous galaxies in pairs at projected
separations of 5-20 kpc out to z=1.2 in the COSMOS field using ACS images and
photometric redshifts derived from an extensive multiwavelength dataset.
Analysis of a complete sample of 106,188 galaxies more luminous than M_V=-19.8
(~ L_V*) in the redshift range 0.1 < z < 1.2 yields 1,749 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 (SDSS). 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 \propto (1+z)^{n=3.1 \pm
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 to
3.
