Galaxy Mergers up to Z < 2.5. I. The Star Formation Properties of Merging Galaxies at Separations of 3-15 kpc

We present a study of the influence of galaxy mergers on star formation at 0.3 < z < 2.5. Major mergers are selected from the CANDELS/3D-HST catalog using a peak-finding algorithm. Mergers have projected galaxy nucleus separation of their members between 3 and 15 kpc. We compare the star formation activity in merging and nonmerging galaxies and find no significant differences. We find that only 12% of the galaxies in major mergers (in which both galaxies have log (M-star/M-circle dot) >= 10) are starbursting (i.e., with star formation rate (SFR) above the main sequence of star-forming galaxies by >0.5 dex). Merging galaxies, which include galaxies with lower masses, show a higher fraction of starbursting galaxies (20%). The low fraction of starbursting merging galaxies in this sample suggests that at galaxy nucleus separations of 3-15 kpc merging galaxies are still in an early stage and are yet to reach the maximum level of star formation activity. Furthermore, the level of star formation enhancement and its duration could be arguably reduced compared to local mergers, as shown by simulations of high-z mergers, and might also depend on the physical properties (such as stellar mass and gas fraction) of the merging galaxies. Finally, we compare the specific SFR between merging galaxies. Our results suggest that, as the mass of the merging galaxies increases, the star formation activity in the less massive member in the merger suffers a more dramatic impact than its companion galaxy.