Great Optically Luminous Dropout Research Using Subaru HSC (GOLDRUSH). I. UV luminosity functions at z ∼ 4–7 derived with the half-million dropouts on the 100 deg2 sky†

We study the UV luminosity functions (LFs) at $z\sim 4$, $5$, $6,$ and $7$ based on the deep large-area optical images taken by the Hyper Suprime-Cam (HSC) Subaru strategic program (SSP). On the 100 deg$^2$ sky of the HSC SSP data available to date, we make enormous samples consisting of a total of 579,565 dropout candidates at $z\sim 4-7$ by the standard color selection technique, 358 out of which are spectroscopically confirmed by our follow-up spectroscopy and other studies. We obtain UV LFs at $z \sim 4-7$ that span a very wide UV luminosity range of $\sim 0.002 - 100 \, L_{\rm UV}^\ast$ ($-26 2 \sigma$ significance, and require either double power-law functions or modified Schechter functions that consider a magnification bias due to gravitational lensing.