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Title: THE SUBARU HIGH-z QUASAR SURVEY: DISCOVERY OF FAINT z ∼ 6 QUASARS

Abstract

We present the discovery of one or two extremely faint z ∼ 6 quasars in 6.5 deg{sup 2} utilizing a unique capability of the wide-field imaging of the Subaru/Suprime-Cam. The quasar selection was made in (i'-z{sub B} ) and (z{sub B} -z{sub R} ) colors, where z{sub B} and z{sub R} are bandpasses with central wavelengths of 8842 Å and 9841 Å, respectively. The color selection can effectively isolate quasars at z ∼ 6 from M/L/T dwarfs without the J-band photometry down to z{sub R} < 24.0, which is 3.5 mag deeper than the Sloan Digital Sky Survey (SDSS). We have selected 17 promising quasar candidates. The follow-up spectroscopy for seven targets identified one apparent quasar at z = 6.156 with M {sub 1450} = –23.10. We also identified one possible quasar at z = 6.041 with a faint continuum of M {sub 1450} = –22.58 and a narrow Lyα emission with HWHM =427 km s{sup –1}, which cannot be distinguished from Lyman α emitters. We derive the quasar luminosity function at z ∼ 6 by combining our faint quasar sample with the bright quasar samples by SDSS and CFHQS. Including our data points invokes a higher number density inmore » the faintest bin of the quasar luminosity function than the previous estimate employed. This suggests a steeper faint-end slope than lower z, though it is yet uncertain based on a small number of spectroscopically identified faint quasars, and several quasar candidates still remain to be diagnosed. The steepening of the quasar luminosity function at the faint end does increase the expected emission rate of the ionizing photon; however, it only changes by a factor of approximately two to six. This was found to still be insufficient for the required photon budget of reionization at z ∼ 6.« less

Authors:
; ;  [1]; ; ; ;  [2];  [3];  [4];  [5];  [6];  [7]
  1. Optical and Infrared Astronomy Division, National Astronomical Observatory, Mitaka, Tokyo 181-8588 (Japan)
  2. Department of Astronomy, School of Science, Graduate University for Advanced Studies, Mitaka, Tokyo 181-8588 (Japan)
  3. Herzberg Institute of Astrophysics, National Research Council, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)
  4. 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 151-742 (Korea, Republic of)
  5. Department of Astronomy, University of Tokyo, Hongo, Tokyo 113-0033 (Japan)
  6. Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8582 (Japan)
  7. Gemini Observatory, La Serena (Chile)
Publication Date:
OSTI Identifier:
22364750
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 798; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; APPROXIMATIONS; COLOR; COSMIC PHOTONS; COSMOLOGY; DWARF STARS; EMISSION SPECTRA; LUMINOSITY; LYMAN LINES; PHOTOMETRY; QUASARS

Citation Formats

Kashikawa, Nobunari, Furusawa, Hisanori, Niino, Yuu, Ishizaki, Yoshifumi, Onoue, Masafusa, Toshikawa, Jun, Ishikawa, Shogo, Willott, Chris J., Im, Myungshin, Shimasaku, Kazuhiro, Ouchi, Masami, and Hibon, Pascale. THE SUBARU HIGH-z QUASAR SURVEY: DISCOVERY OF FAINT z ∼ 6 QUASARS. United States: N. p., 2015. Web. doi:10.1088/0004-637X/798/1/28.
Kashikawa, Nobunari, Furusawa, Hisanori, Niino, Yuu, Ishizaki, Yoshifumi, Onoue, Masafusa, Toshikawa, Jun, Ishikawa, Shogo, Willott, Chris J., Im, Myungshin, Shimasaku, Kazuhiro, Ouchi, Masami, & Hibon, Pascale. THE SUBARU HIGH-z QUASAR SURVEY: DISCOVERY OF FAINT z ∼ 6 QUASARS. United States. https://doi.org/10.1088/0004-637X/798/1/28
Kashikawa, Nobunari, Furusawa, Hisanori, Niino, Yuu, Ishizaki, Yoshifumi, Onoue, Masafusa, Toshikawa, Jun, Ishikawa, Shogo, Willott, Chris J., Im, Myungshin, Shimasaku, Kazuhiro, Ouchi, Masami, and Hibon, Pascale. 2015. "THE SUBARU HIGH-z QUASAR SURVEY: DISCOVERY OF FAINT z ∼ 6 QUASARS". United States. https://doi.org/10.1088/0004-637X/798/1/28.
@article{osti_22364750,
title = {THE SUBARU HIGH-z QUASAR SURVEY: DISCOVERY OF FAINT z ∼ 6 QUASARS},
author = {Kashikawa, Nobunari and Furusawa, Hisanori and Niino, Yuu and Ishizaki, Yoshifumi and Onoue, Masafusa and Toshikawa, Jun and Ishikawa, Shogo and Willott, Chris J. and Im, Myungshin and Shimasaku, Kazuhiro and Ouchi, Masami and Hibon, Pascale},
abstractNote = {We present the discovery of one or two extremely faint z ∼ 6 quasars in 6.5 deg{sup 2} utilizing a unique capability of the wide-field imaging of the Subaru/Suprime-Cam. The quasar selection was made in (i'-z{sub B} ) and (z{sub B} -z{sub R} ) colors, where z{sub B} and z{sub R} are bandpasses with central wavelengths of 8842 Å and 9841 Å, respectively. The color selection can effectively isolate quasars at z ∼ 6 from M/L/T dwarfs without the J-band photometry down to z{sub R} < 24.0, which is 3.5 mag deeper than the Sloan Digital Sky Survey (SDSS). We have selected 17 promising quasar candidates. The follow-up spectroscopy for seven targets identified one apparent quasar at z = 6.156 with M {sub 1450} = –23.10. We also identified one possible quasar at z = 6.041 with a faint continuum of M {sub 1450} = –22.58 and a narrow Lyα emission with HWHM =427 km s{sup –1}, which cannot be distinguished from Lyman α emitters. We derive the quasar luminosity function at z ∼ 6 by combining our faint quasar sample with the bright quasar samples by SDSS and CFHQS. Including our data points invokes a higher number density in the faintest bin of the quasar luminosity function than the previous estimate employed. This suggests a steeper faint-end slope than lower z, though it is yet uncertain based on a small number of spectroscopically identified faint quasars, and several quasar candidates still remain to be diagnosed. The steepening of the quasar luminosity function at the faint end does increase the expected emission rate of the ionizing photon; however, it only changes by a factor of approximately two to six. This was found to still be insufficient for the required photon budget of reionization at z ∼ 6.},
doi = {10.1088/0004-637X/798/1/28},
url = {https://www.osti.gov/biblio/22364750}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 798,
place = {United States},
year = {Thu Jan 01 00:00:00 EST 2015},
month = {Thu Jan 01 00:00:00 EST 2015}
}