SILVERRUSH. IV. Lyα luminosity functions at z = 5.7 and 6.6 studied with ∼1300 Lyα emitters on the 14-21 deg2 sky

Akira Konno, Masami Ouchi, Takatoshi Shibuya, Yoshiaki Ono, Kazuhiro Shimasaku, Yoshiaki Taniguchi, Tohru Nagao, Masakazu A.R. Kobayashi, Masaru Kajisawa, Nobunari Kashikawa, Akio K. Inoue, Masamune Oguri, Hisanori Furusawa, Tomotsugu Goto, Yuichi Harikane, Ryo Higuchi, Yutaka Komiyama, Haruka Kusakabe, Satoshi Miyazaki, Kimihiko NakajimaShiang Yu Wang

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136 Citations (Scopus)


We present the Lyα luminosity functions (LFs) at z = 5.7 and 6.6 derived from a new large sample of 1266 Lyα emitters (LAEs) identified in total areas of 14 and 21 deg2, respectively, based on the early narrowband data of the Subaru/Hyper Suprime-Cam survey. Together with careful Monte Carlo simulations that account for the incompleteness of the LAE selection and the flux estimate systematics in the narrowband imaging, we have determined the Lyα LFs with unprecedentedly small statistical and systematic uncertainties in a wide Lyα luminosity range of 1042.8-43.8 erg s-1. We obtain best-fit Schechter parameters of L∗Lyα = 1.6-0.6+2.2 (1.7-0.7+0.3) × 1043 erg s-1, φ∗Lyα = 0.85-0.77+1.87 (0.47-0.44+1.44) × 10-4 Mpc-3, and α = -2.6-0.4+0.6 (-2.5-0.5+0.5) at z = 5.7 (6.6). We confirm that our best-estimate Lyα LFs are consistent with the majority of the previous studies, but find that our Lyα LFs do not agree with the high number densities of LAEs recently claimed by Matthee/Santos et al.'s studies that may overcorrect the incompleteness and the flux systematics. Our Lyα LFs at z = 5.7 and 6.6 show an indication that the faint-end slope is very steep (α - -2.5), although it is also possible that the bright-end LF results are enhanced by systematic effects such as the contribution from AGNs, blended merging galaxies, and/or large ionized bubbles around bright LAEs. Comparing our Lyα LF measurements with four independent reionization models, we estimate the neutral hydrogen fraction of the intergalactic medium to be xHI = 0.3 ± 0.2 at z = 6.6, which is consistent with the small Thomson scattering optical depth obtained by Planck 2016.

Original languageEnglish
Article numberS16
JournalPublications of the Astronomical Society of Japan
Issue numberSpecial Issue 1
Publication statusPublished - 2018 Jan 1
Externally publishedYes


  • Cosmology
  • First stars-galaxies
  • Formation-galaxies
  • High-redshift-galaxies
  • Luminosity function
  • Mass function
  • Observations-dark ages
  • Reionization

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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