Quasar Luminosity Function at z = 7

Abstract We present the quasar luminosity function (LF) at z = 7, measured with 35 spectroscopically confirmed quasars at 6.55 M 1450 * = − 25.60 − 0.30 + 0.40 , a characteristic density Φ * = 1.35 − 0.30 + 0.47 Gpc −3 mag −1 , and a bright-end slope β = − 3.34 − 0.57 + 0.49 , when the faint-end slope is fixed to α = −1.2 as observed at z ≤ 6. The overall LF shape remains remarkably similar from z = 4 to 7, while the amplitude decreases substantially toward higher redshifts, with a clear indication of an accelerating decline at z ≥ 6. The estimated ionizing photon density, 10 48.2±0.1 s −1 Mpc −3 , is less than 1% of the critical rate to keep the intergalactic medium ionized at z = 7, and thus indicates that quasars are not a major contributor to cosmic reionization.