A Slow Merger History of Field Galaxies since z ~ 1

Using deep infrared observations conducted with the CISCO imager on theSubaru Telescope, we investigate the field-corrected pair fraction and theimplied merger rate of galaxies in redshift survey fields with Hubble SpaceTelescope imaging. In the redshift interval, 0.5 < z < 1.5, the fraction ofinfrared-selected pairs increases only modestly with redshift to 7% +- 6% atz~1. This is nearly a factor of three less than the fraction, 22% +- 8%,determined using the same technique on HST optical images and as measured in aprevious similar study. Tests support the hypothesis that optical pairfractions at z~1 are inflated by bright star-forming regions that are unlikelyto be representative of the underlying mass distribution. By determiningstellar masses for the companions, we estimate the mass accretion rateassociated with merging galaxies. At z~1, we estimate this to be 2x10^{9 +-0.2} solar masses per galaxy per Gyr. Although uncertainties remain, ourresults suggest that the growth of galaxies via the accretion of pre-existingfragments remains as significant a phenomenon in the redshift range studied asthat estimated from ongoing star formation in independent surveys.Comment: 5 pages, accepted for publication in ApJ Letter