Galaxy Morphologies Revealed with Subaru HSC and Super-Resolution
  Techniques I: Major Merger Fractions of L_UV~3-15 L_UV* Dropout Galaxies at
  z~4-7
  We perform a super-resolution analysis of the Subaru Hyper Suprime-Cam (HSC)
images to estimate the major merger fractions of z~4-7 dropout galaxies at the
bright end of galaxy UV luminosity functions (LFs). Our super-resolution
technique improves the spatial resolution of the ground-based HSC images, from
~1" to <~0."1, which is comparable to that of the Hubble Space Telescope,
allowing us to identify z~4-7 bright major mergers at a high completeness value
of >~90%. We apply the super-resolution technique to 6412, 16, 94, and 13 very
bright dropout galaxies at z~4, 5, 6, and 7, respectively, in a UV luminosity
range of L_UV~3-15 L_UV* corresponding to -24<~M_UV<~-22. The major merger
fractions are estimated to be f_merger~10-20% at z~4 and ~50-70% at z~5-7,
which shows no f_merger difference compared to those of a control faint galaxy
sample. Based on the f_merger estimates, we verify contributions of source
blending effects and major mergers to the bright-end of double power-law (DPL)
shape of z~4-7 galaxy UV LFs. While these two effects partly explain the DPL
shape at L_UV~3-10 L_UV*, the DPL shape cannot be explained at the very bright
end of L_UV>~10 L_UV*, even after the AGN contribution is subtracted. The
results support scenarios in which other additional mechanisms such as
insignificant mass quenching and low dust obscuration contribute to the DPL
shape of galaxy UV LFs.
