Quasar Luminosity Function at z = 7

Yoshiki Matsuoka, Masafusa Onoue, K. Iwasawa, Michael A. Strauss, Nobunari Kashikawa, Takuma Izumi, Tohru Nagao, Masatoshi Imanishi, Masayuki Akiyama, J. D. Silverman

Abstract

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 <?CDATA ${M}_{1450}^{* }=-{25.60}_{-0.30}^{+0.40}$?> <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 <?CDATA ${{\rm{\Phi }}}^{* }={1.35}_{-0.30}^{+0.47}$?> <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 <?CDATA $\beta =-{3.34}_{-0.57}^{+0.49}$?> <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.

Locations

• The Astrophysical Journal Letters - View - PDF
• arXiv (Cornell University) - View - PDF