A New Constraint on the Lyα Fraction of UV Very Bright Galaxies at Redshift 7

Hisanori Furusawa, Nobunari Kashikawa, Masakazu A. R. Kobayashi, James S. Dunlop, Kazuhiro Shimasaku, Tadafumi Takata, Kazuhiro Sekiguchi, Yoshiaki Naito, Junko Furusawa, Masami Ouchi, Fumiaki Nakata, Naoki Yasuda, Yuki Okura, Yoshiaki Taniguchi, Toru Yamada, Masaru Kajisawa, Johan P. U. Fynbo, Olivier Le Fèvre

Research output: Contribution to journalArticlepeer-review


We study the extent to which very bright (-23.0\lt {M}{UV}\lt -21.75) Lyman-break-selected galaxies at redshifts z≃ 7 display detectable Lyα emission. To explore this issue, we obtained follow-up optical spectroscopy of 9 z≃ 7 galaxies from a parent sample of 24 z≃ 7 galaxy candidates selected from the 1.65 deg2 COSMOS-UltraVISTA and SXDS-UDS survey fields using the latest near-infrared public survey data, and new ultra-deep Subaru z‧-band imaging (which we also present and describe in this paper). Our spectroscopy yielded only one possible detection of Lyα at z = 7.168 with a rest-frame equivalent width {{EW}}0 = {3.7}-1.1+1.7 \mathringA . The relative weakness of this line, combined with our failure to detect Lyα emission from the other spectroscopic targets, allows us to place a new upper limit on the prevalence of strong Lyα emission at these redshifts. For conservative calculation and to facilitate comparison with previous studies at lower redshifts, we derive a 1σ upper limit on the fraction of UV-bright galaxies at z≃ 7 that display {{EW}}0\gt 50 \mathringA , which we estimate to be \lt 0.23. This result may indicate a weak trend where the fraction of strong Lyα emitters ceases to rise, and possibly falls between z ≃ 6 and z≃ 7. Our results also leave open the possibility that strong Lyα may still be more prevalent in the brightest galaxies in the reionization era than their fainter counterparts. A larger spectroscopic sample of galaxies is required to derive a more reliable constraint on the neutral hydrogen fraction at z∼ 7 based on the Lyα fraction in the bright galaxies.
Original languageEnglish
Pages (from-to)46
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 3 May 2016


  • cosmology: observations
  • dark ages
  • reionization
  • first stars
  • galaxies: evolution
  • galaxies: high-redshift


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