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 &lt; z &lt; 7.15. The sample of 22 quasars from the Subaru High- z Exploration of Low-Luminosity Quasars (SHELLQs) project, combined with 13 brighter quasars in the literature, covers an unprecedentedly wide range of rest-frame ultraviolet magnitudes over −28 &lt; M 1450 &lt; −23. We found that the binned LF flattens significantly toward the faint end populated by the SHELLQs quasars. A maximum likelihood fit to a double power-law model has a break magnitude <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>1450</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>25.60</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.30</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.40</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> , a characteristic density <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">Φ</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msup> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>1.35</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.30</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.47</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> Gpc −3 mag −1 , and a bright-end slope <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>β</mml:mi> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>3.34</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.57</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.49</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> , 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.