Minor Contribution of Quasars to Ionizing Photon Budget at z ∼ 6: Update on Quasar Luminosity Function at the Faint End with Subaru/Suprime-Cam
- Department of Astronomical Science, Graduate University for Advanced Studies (SOKENDAI), 2-21-1, Osawa, Mitaka, Tokyo 181-8588 (Japan)
- Herzberg Institute of Astrophysics, National Research Council, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)
- European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago (Chile)
- Center for the Exploration of the Origin of the Universe (CEOU), Astronomy Program, Department of Physics and Astronomy, Seoul National University, 1-Gwanak-rho, Gwanak-gu, Seoul 141-742 (Korea, Republic of)
- National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, Tokyo 181-8588 (Japan)
- Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8582 (Japan)
- Research Center for Space and Cosmic Evolution, Ehime University, Matsuyama, Ehime 790-8577 (Japan)
- Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 10617, Taiwan (China)
We constrain the quasar contribution to the cosmic reionization based on our deep optical survey of z ∼ 6 quasars down to z {sub R} = 24.15 using Subaru/Suprime-Cam in three UKIDSS-DXS fields covering 6.5 deg{sup 2}. In Kashikawa et al. (2015), we select 17 quasar candidates and report our initial discovery of two low-luminosity quasars (M{sub 1450}∼−23) from seven targets, one of which might be a Lyα-emitting galaxy. From an additional optical spectroscopy, none of the four candidates out of the remaining 10 turn out to be genuine quasars. Moreover, the deeper optical photometry provided by the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) shows that, unlike the two already-known quasars, the i − z and z − y colors of the last six candidates are consistent with M- or L-type brown dwarfs. Therefore, the quasar luminosity function (QLF) measurement in the previous paper is confirmed. Compiling the QLF measurements from the literature over a wide magnitude range, including an extremely faint AGN candidate from Parsa et al. (2017), to fit them with a double power law, we find that the best-fit faint-end slope is α=−2.04{sub −0.18}{sup +0.33} (−1.98{sub −0.21}{sup +0.48}) and characteristic magnitude is M{sub 1450}{sup ∗}=−25.8{sub −1.9}{sup +1.1} (−25.7{sub −1.8}{sup +1.0}) in the case of two (one) quasar detection. Our result suggests that, if the QLF is integrated down to M{sub 1450}=−18, quasars produce ∼1%–12% of the ionizing photons required to fully ionize the universe at z ∼ 6 with a 2σ confidence level, assuming that the escape fraction is f{sub esc}=1 and the intergalactic medium clumpy factor is C = 3. Even when the systematic uncertainties are taken into account, our result supports the scenario that quasars are the minor contributors of the reionization.
- OSTI ID:
- 22872539
- Journal Information:
- Astrophysical Journal Letters, Vol. 847, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United Kingdom
- Language:
- English
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