Galaxy morphologies revealed with Subaru HSC and super-resolution techniques. II. Environmental dependence of galaxy mergers at z ∼ 2-5

We super-resolve the seeing-limited Subaru Hyper Suprime-Cam (HSC) images for 32187 galaxies at similar to 2-5 using three techniques, namely, the classical Richardson-Lucy (RL) point spread function (PSF) deconvolution, sparse modeling, and generative adversarial networks, to investigate the environmental dependence of galaxy mergers. These three techniques generate overall similar high spatial resolution images but with some slight differences in galaxy structures; for example, more residual noises are seen in the classical RL PSF deconvolution. To alleviate the disadvantages of each technique, we create combined images by averaging over the three types of super-resolution images, resulting in galaxy substructures resembling those seen in the Hubble Space Telescope images. Using the combined super-resolution images, we measure the relative galaxy major merger fraction corrected for the chance projection effect, f (rel,col) (merger), for galaxies in the similar to 300 deg(2) area data of the HSC Strategic Survey Program and the CFHT Large Area U-band Survey. Our f (rel,col) (merger) measurements at z similar to 3 validate previous findings showing that f (rel,col) (merger) is higher in regions with a higher galaxy overdensity delta at z similar to 2-3. Thanks to the large galaxy sample, we identify a nearly linear increase in f (rel,col) (merger) with increasing delta at z similar to 4-5, providing the highest-z observational evidence that galaxy mergers are related to delta . In addition to our f (rel,col) (merger) measurements, we find that the galaxy merger fractions in the literature also broadly align with the linear f (rel,col) (merger) delta relation across a wide redshift range of z similar to 2-5. This alignment suggests that the linear f (rel,col) (merger) delta relation can serve as a valuable tool for quantitatively estimating the contributions of galaxy mergers to various environmental dependences. This super-resolution analysis can be readily applied to datasets from wide field-of-view space telescopes such as Euclid and Roman.