Galaxy Merger Fractions in Two Clusters at z similar to 2 Using the Hubble Space Telescope

Abstract

We measure the fraction of galaxy-galaxy mergers in two clusters at z similar to 2 using imaging and grism observations from the Hubble Space Telescope. The two galaxy cluster candidates were originally identified as overdensities of objects using deep mid-infrared imaging and observations from the Spitzer Space Telescope, and were subsequently followed up with HST/WFC3 imaging and grism observations. We identify galaxy-galaxy merger candidates using high-resolution imaging with the WFC3 in the F105W, F125W, and F160W bands. Coarse redshifts for the same objects are obtained with grism observations in G102 for the z similar to 1.6 cluster (IRC0222A) and G141 for the z similar to 2 cluster (IRC0222B). Using visual classifications as well as a variety of selection techniques, we measure merger fractions of 11(-3.2)(+8.2) in IRC0222A and 18(-4.5)(+7.8) in IRC0222B. In comparison, we measure a merger fraction of 5.0(-0.8)(+1.1)% for field galaxies at z similar to 2. Our study indicates that the galaxy-galaxy merger fraction in clusters at z similar to 2 is enhanced compared to the field population, but note that more cluster measurements at this epoch are needed to confirm our findings.