“Big three dragons”: a z = 7.15 lyman break galaxy detected in [Oiii] 88 µm, [Cii] 158 µm, and dust continuum with alma

Takuya Hashimoto, Akio K. Inoue, Ken Mawatari, Yoichi Tamura, Hiroshi Matsuo, Hisanori Furusawa, Yuichi Harikane, Takatoshi Shibuya, Kirsten K. Knudsen, Kotaro Kohno, Yoshiaki Ono, Erik Zackrisson, Takashi Okamoto, Nobunari Kashikawa, Pascal A. Oesch, Masami Ouchi, Kazuaki Ota, Ikkoh Shimizu, Yoshiaki Taniguchi, Hideki UmehataDarach Watson

Research output: Contribution to journalArticlepeer-review


We present new ALMA observations and physical properties of a Lyman Break Galaxy at z = 7.15. Our target, B14-65666, has a bright ultra-violet (UV) absolute magnitude, MUV ≈ −22.4, and has been spectroscopically identified in Lyα with a small rest-frame equivalent width of ≈ 4 Å. Previous HST image has shown that the target is comprised of two spatially separated clumps in the rest-frame UV. With ALMA, we have newly detected spatially resolved [Oiii] 88 µm, [Cii] 158 µm, and their underlying dust continuum emission. In the whole system of B14-65666, the [Oiii] and [Cii] lines have consistent redshifts of 7.1520 ± 0.0003, and the [Oiii] luminosity, (34.4 ± 4.1) × 108 L☉, is about three times higher than the [Cii] luminosity, (11.0 ± 1.4) × 108 L☉. With our two continuum flux densities, the dust temperature is constrained to be Td ≈ 50 − 60 K under the assumption of the dust emissivity index of βd = 2.0 − 1.5, leading to a large total infrared luminosity of LTIR ≈ 1 × 1012 L☉. Owing to our high spatial resolution data, we show that the [Oiii] and [Cii] emission can be spatially decomposed into two clumps associated with the two rest-frame UV clumps whose spectra are kinematically separated by ≈ 200 km s−1. We also find these two clumps have comparable UV, infrared, [Oiii], and [Cii] luminosities. Based on these results, we argue that B14-65666 is a starburst galaxy induced by a major-merger. The merger interpretation is also supported by the large specific star-formation rate (defined as the star-formation rate per unit stellar mass), sSFR = 260+119−57 Gyr−1, inferred from our SED fitting. Probably, a strong UV radiation field caused by intense star formation contributes to its high dust temperature and the [Oiii]-to-[Cii] luminosity ratio.

Original languageEnglish
JournalUnknown Journal
Publication statusPublished - 2018 Jun 1


  • Galaxies: formation
  • Galaxies: high-redshift
  • Galaxies: ISM

ASJC Scopus subject areas

  • General

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