The Faint End of the Quasar Luminosity Function at $z\sim 5$ from the Subaru Hyper Suprime-Cam Survey

Abstract

We present the quasar luminosity function at $z\sim 5$ derived from the optical wide-field survey data obtained as a part of the Subaru strategic program (SSP) with Hyper Suprime-Cam (HSC). From $\sim$81.8 deg${}^2$ area in the Wide layer of the HSC-SSP survey, we selected 224 candidates of low-luminosity quasars at $z\sim 5$ 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 $z\sim 5$ covering a wide luminosity range of $-28.76<M_{1450}<-22.32$ mag. We found that the quasar luminosity function is fitted by a double power-law model with a break magnitude of $M_{1450}^{\ast }=-25.05_{-0.24}^{+0.10}$ 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 $z\sim 5$. A compilation of the quasar luminosity function at $4\le z\le 6$ 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 $z\sim 5$ to $z\sim 6$ than from $z\sim 4$ to $z\sim 5$.

18 pages, 11 figures, accepted for publication in ApJ

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