Subaru/HSC deep optical imaging of infrared sources in the AKARI North Ecliptic Pole-Wide field

Abstract

We present a five-broad-band (grizy) photometric catalogue of Subaru/Hyper Suprime-Cam (HSC) optical imaging observations at around the North Ecliptic Pole (NEP) where the AKARI infrared (IR) satellite conducted a large survey (NEP-Wide survey). The observations cover almost all the NEP-Wide survey field down to the depth of 28.1, 26.8, 26.3, 25.5, and 25.0 mag (5σ) at grizy, respectively. The five-band HSC catalogue contains about 2.6 million objects, and 70 959 AKARI NEP-Wide counterpart sources are identified in the catalogue. We added existing supplementary catalogues from the u band to the far-IR band, and estimated photo-z for the AKARI-HSC sources. We achieved σ_{Δz/(1 + zs)} = 0.06 and an outlier rate of 13.4 per cent at z = 0.2-1.5. Using the spectral energy distribution (SED) template fitting, we classified the AKARI-HSC galaxies into four categories, namely quiescent, star-forming, Type1 active galactic nucleus (AGN), and Type2 AGN, in each redshift bin. At z > 1, the mean SED of star-forming galaxies in mid-IR (3-10 μm) range is significantly different from that of spiral galaxies in the nearby Universe, indicating that many of star-forming galaxies at z > 1 contain a heat source capable of heating dust to temperatures that radiate thermal emission in the mid-IR range. Furthermore, we estimated the number fraction of AGNs (f_AGN) in each bin of redshift and IR luminosity (L_IR), and examined the dependence of redshift and L_IR. In log(L_IR/L_⊙) = 11.0-14.0, the f_AGN shows a significant increase with increasing redshift, regardless of the L_IR bins. In contrast, the f_AGN shows a slight increase against L_IR at z < 1 and no increase with increasing L_IR at z > 1.