Direct evidence for Lyα depletion in the protocluster core

Rhythm Shimakawa, Tadayuki Kodama, Masao Hayashi, Ichi Tanaka, Yuichi Matsuda, Nobunari Kashikawa, Takatoshi Shibuya, Ken Ichi Tadaki, Yusei Koyama, Tomoko L. Suzuki, Moegi Yamamoto

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25 Citations (Scopus)


We have carried out panoramic Lyα narrow-band imaging with Suprime-Cam on Subaru towards the known protocluster USS1558-003 at z = 2.53. Our previous narrow-band imaging in the near-infrared identified multiple dense groups of Ha emitters (HAEs) within the protocluster. We have now identified the large-scale structures across a ~50 comoving Mpc scale traced by Lyα emitters (LAEs) in which the protocluster traced by the HAEs is embedded. On a smaller scale, however, there are remarkably few LAEs in the regions of HAE overdensities. Moreover, the stacking analyses of the images show that HAEs in higher-density regions show systematically lower escape fractions of Lyα photons than those of HAEs in lower-density regions. These phenomena may be driven by the extra depletion of Lyα emission lines along our line of sight by more intervening cold circumgalactic/intergalactic medium and/or dust in the dense core.We also caution that all the previous high-z protocluster surveys using LAEs as tracers would have largely missed galaxies in the very dense cores of the protoclusters where we would expect to see any early environmental effects.

Original languageEnglish
Pages (from-to)L21-L25
JournalMonthly Notices of the Royal Astronomical Society: Letters
Issue number1
Publication statusPublished - 2017 Jun


  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: high-redshift


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