Evolution of the Frequency of Luminous (≥ aastex amsbsy amsfonts amssymb bm mathrsfs pifont stmaryrd textcomp portland, xspace amsmath, amsxtra 2, OT1fontenc wncyr 2 empty 10976 document L^ₕ document) 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 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 MV=-19. 8 (~ LV*) 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 (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 to 3.