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 M_V=-19.8 (~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.

Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555 also based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan; Kitt Peak National Observatory, Cerro Tololo Inter-American Observatory, and the National Optical Astronomy Observatory, which are operated by AURA, Inc., under cooperative agreement with the National Science Foundation; and the Canada-France-Hawaii Telescope, operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique de France, and the University of Hawaii.