Environmental impacts on molecular gas in protocluster galaxies at z ∼ 2

Ken Ichi Tadaki, Tadayuki Kodama, Masao Hayashi, Rhythm Shimakawa, Yusei Koyama, Minju Lee, Ichi Tanaka, Bunyo Hatsukade, Daisuke Iono, Kotaro Kohno, Yuichi Matsuda, Tomoko Suzuki, Yoichi Tamura, Jun Toshikawa, Hideki Umehata

Research output: Contribution to journalArticlepeer-review

34 Citations (Scopus)


We present the results from ALMA CO(3-2) observations of 66 Hα-selected galaxies in three protoclusters around radio galaxies: PKS 1138-262 (z = 2.16), USS 1558-003 (z = 2.53), and 4C 23.56 (z = 2.49). The pointing areas have an overdensity of ∼100 compared to the mean surface number density of galaxies in field environments. We detect the CO emission line in 16 star-forming galaxies, including six previously published galaxies, to measure the molecular gas mass. In the stellar mass range of 10.5 < log (Mstar/M) < 11.0, the protocluster galaxies have larger gas mass fractions and longer gas depletion timescales compared to the scaling relations established for field galaxies. On the other hand, the amounts of molecular gas in more massive galaxies with log (Mstar/M) > 11.0 are comparable in mass to the scaling relation, or smaller. Our results suggest that the environmental effects on gas properties are mass dependent: in high-density environments, gas accretion through cosmic filaments is accelerated in less massive galaxies, while this is suppressed in the most massive system.

Original languageEnglish
Article number40
JournalPublications of the Astronomical Society of Japan
Issue number2
Publication statusPublished - 2019 Apr 1


  • Galaxies: ISM
  • Galaxies: clusters: general
  • Galaxies: high-redshift

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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