Evidence for a gas-rich major merger in a proto-cluster at z = 2.5

Ken Ichi Tadaki, Tadayuki Kodama, Yoichi Tamura, Masao Hayashi, Yusei Koyama, Rhythm Shimakawa, Ichi Tanaka, Kotaro Kohno, Bunyo Hatsukade, Kenta Suzuki

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)


Gas-rich major mergers in high-redshift proto-clusters are important events, perhaps leading to the creation of the slowly rotating remnants seen in the cores of clusters in the present day. Here, we present a deep Jansky Very Large Array observation of CO J = 1-0 emission line in a proto-cluster at z = 2.5, USS1558-003. The target field is an extremely dense region, where 20 Hα emitters (HAEs) are clustering. We have successfully detected the CO emission line from three HAEs and discovered a close pair of red and blue CO-emitting HAEs. Given their close proximity (30 kpc), small velocity offset (300 km s-1), and similar stellar masses, they could be in the early phase of a gas-rich major merger. For the red HAE, we derive a total infrared luminosity of L IR = 5.1 × 1012 L using MIPS 24 μm and radio continuum images. The ratio is significantly enhanced compared to local spirals and high-redshift disks with a similar CO luminosity, which is indicative of a starburst mode. We find the gas depletion timescale is shorter than that of normal star-forming galaxies regardless of adopted CO-H2 conversion factors. The identification of such a rare event suggests that gas-rich major mergers frequently take place in proto-clusters at z > 2 and may involve the formation processes of slow rotators seen in local massive clusters.

Original languageEnglish
Article numberL23
JournalAstrophysical Journal Letters
Issue number2
Publication statusPublished - 2014 Jun 20
Externally publishedYes


  • galaxies: ISM
  • galaxies: evolution
  • galaxies: high-redshift

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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