Galaxy morphologies revealed with Subaru HSC and super-resolution techniques. I. Major merger fractions of LUV ∼ 3-15 LUV* 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 similar to 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 similar to 1 '' to less than or similar to 0.'' 1, which is comparable to that of the Hubble Space Telescope, allowing us to identify z similar to 4-7 bright major mergers at a high completeness value of greater than or similar to 90%. We apply the super-resolution technique to 6412, 16, 94, and 13 very bright dropout galaxies at z similar to 4, 5, 6, and 7, respectively, in a UV luminosity range of L-UV similar to 3-15 L-UV* corresponding to -24 less than or similar to M-UV less than or similar to -22. The major merger fractions are estimated to be f(merger) similar to 10%-20% at z similar to 4 and similar to 50%-70% at z similar to 5-7, which shows no f 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 similar to 4-7 galaxy UV LFs. While these two effects partly explain the DPL shape at L-UV similar to 3-10 L-UV*, the DPL shape cannot be explained at the very bright end of L-UV greater than or similar to 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.

Automated summary

We performed a super-resolution analysis of Subaru Hyper Suprime-Cam (HSC) images and estimated the major merger fractions of z similar to 4-7 dropout galaxies at the bright end of galaxy UV luminosity functions (LFs). The major merger fractions were found to be around 10%-20% at z similar to 4 and 50%-70% at z similar to 5-7.