2020ApJ...904...89N

We present the quasar luminosity function at z ∼ 5 derived from the optical wide-field survey data obtained as a part of the Subaru strategic program (SSP) with the Hyper Suprime-Cam (HSC). From a ∼81.8 deg² area in the Wide layer of the HSC-SSP survey, we selected 224 candidates of low-luminosity quasars at z ∼ 5 by adopting the Lyman-break method down to i = 24.1 mag. Based on our candidates and spectroscopically confirmed quasars from the Sloan Digital Sky Survey (SDSS), we derived the quasar luminosity function at z ∼ 5, covering a wide luminosity range of -28.76 < M₁₄₅₀ < -22.32 mag. We found that the quasar luminosity function is fitted by a double power-law model with a break magnitude of M₁₄₅₀^* =-25.05_–0.24^+0.10 mag. The inferred number density of low-luminosity quasars is lower, and the derived faint-end slope, -1.22_–0.10^+0.03, is flatter than those of previous studies at z ∼ 5. A compilation of the quasar luminosity function at 4 <= z <= 6 from the HSC-SSP suggests that there is little redshift evolution in the break magnitude and in the faint-end slope within this redshift range, although previous studies suggest that the faint-end slope becomes steeper at higher redshifts. The number density of low-luminosity quasars decreases more rapidly from z ∼ 5 to z ∼ 6 than from z ∼ 4 to z ∼ 5.