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Using mass-selected galaxy samples from deep multiwavelength data weinvestigate the incidence of close galaxy pairs between z=0.4-2. Many suchclose pairs will eventually merge, and the pair fraction is therefore relatedto the merger rate. Over this redshift range the mean pair fraction isessentially constant (evolving as f_pair (1+z)^{-0.4 +/- 0.6}) with about6+/-1% of massive galaxies having a 1:4 or greater companion within 30h^-1 kpc.Assuming the timescale over which pairs merge is not a strong function ofredshift, this implies a similarly constant merger rate (per unit time) out toz=2. Since about three times as much cosmic time passes at z<1 as betweenz=1-2, this implies that correspondingly more mergers occur in the low-redshiftuniverse. When minor companions (1:10 mass ratio or greater) are included, thepair fraction increases to ~20% and still does not evolve strongly withredshift. We also use a rest-frame color criterion to select pairs containingonly quiescent galaxies (major "dry merger" progenitors), and find them to besimilarly rare and constant with 4-7% of massive quiescent galaxies exhibitinga nearby companion. Thus, even though other studies find major mergers to berelatively uncommon since z=1, our results suggest that few additional mergersoccur in the 1<z<2 range and other mechanisms may be required to explain themass and size growth of galaxies over this epoch.

The diminishing importance of major galaxy mergers at higher redshifts