First Results from the Lyman Alpha Galaxies in the Epoch of Reionization (LAGER) Survey: Cosmological Reionization at z ∼ 7

Zhen Ya Zheng, Junxian Wang, James Rhoads, Leopoldo Infante, Sangeeta Malhotra, Weida Hu, Alistair R. Walker, Linhua Jiang, Chunyan Jiang, Pascale Hibon, Alicia Gonzalez, Xu Kong, Xianzhong Zheng, Gaspar Galaz, L. Felipe Barrientos

Research output: Contribution to journalArticle

44 Scopus citations

Abstract

We present the first results from the ongoing Lyman Alpha Galaxies in the Epoch of Reionization (LAGER) project, which is the largest narrowband survey for z ∼ 7 galaxies to date. Using a specially built narrowband filter NB964 for the superb large-Area Dark Energy Camera (DECam) on the NOAO/CTIO 4 m Blanco telescope, LAGER has collected 34 hr NB964 narrowband imaging data in the 3 deg2 COSMOS field. We have identified 23 Lyα Emitter candidates at z = 6.9 in the central 2-deg2 region, where DECam and public COSMOS multi-band images exist. The resulting luminosity function (LF) can be described as a Schechter function modified by a significant excess at the bright end (four galaxies with L Lyα ∼ 1043.4±0.2 erg s-1). The number density at L Lyα ∼ 1043.4±0.2 erg s-1 is little changed from z = 6.6, while at fainter L Lyα it is substantially reduced. Overall, we see a fourfold reduction in Lyα luminosity density from z = 5.7 to z = 6.9. Combined with a more modest evolution of the continuum UV luminosity density, this suggests a factor of ∼3 suppression of Lyα by radiative transfer through the z ∼ 7 intergalactic medium (IGM). It indicates an IGM neutral fraction of x Hi ∼ 0.4-0.6 (assuming Lyα velocity offsets of 100-200 km s-1). The changing shape of the Lyα LF between z ≲ 6.6 and z = 6.9 supports the hypothesis of ionized bubbles in a patchy reionization at z ∼ 7.

Original languageEnglish (US)
Article numberL22
JournalAstrophysical Journal Letters
Volume842
Issue number2
DOIs
StatePublished - Jun 20 2017

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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