Big Three Dragons: A z=7.15 Lyman-break galaxy detected in [Oiii] 88 mu m, [Cii] 158 mu m, and dust continuum with ALMA
Journal article, 2019

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, M-UV approximate to -22.4, and has been spectroscopically identified in Ly alpha with a small rest-frame equivalent width of approximate to 4 angstrom. A previous Hubble Space TElescope (HST) image has shown that the target is composed of two spatially separated clumps in the rest-frame UV. With ALMA, we have newly detected spatially resolved [Oiii] 88 mu m, [Cii] 158 mu m, 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)x 10(8)L(circle dot), is about three times higher than the [Cii] luminosity, (11.0 +/- 1.4) x 10(8)L(circle dot). With our two continuum flux densities, the dust temperature is constrained to be T-d approximate to 50-60K under the assumption of a dust emissivity index of beta(d) = 2.0-1.5, leading to a large total infrared luminosity of L-TIR approximate to 1 x 10(12)L(circle dot). 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 approximate to 200kms(-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 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.

galaxies: high-redshift

galaxies: formation

galaxies: ISM


Takuya Hashimoto

Waseda University

National Astronomical Observatory of Japan

Osaka Sangyo University

Akio K. Inoue

Osaka Sangyo University

Ken Mawatari

University of Tokyo

Osaka Sangyo University

Yoichi Tamura

Nagoya University

Hiroshi Matsuo

The Graduate University for Advanced Studies (SOKENDAI)

National Astronomical Observatory of Japan

Hisanori Furusawa

National Astronomical Observatory of Japan

Yuichi Harikane

University of Tokyo

Takatoshi Shibuya

Kitami Institute of Technology

Kirsten Kraiberg Knudsen

Chalmers, Space, Earth and Environment, Onsala Space Observatory

Kotaro Kohno

University of Tokyo

Yoshiaki Ono

University of Tokyo

Erik Zackrisson

Uppsala University

Takashi Okamoto

Hokakido University

Nobunari Kashikawa

National Astronomical Observatory of Japan

University of Tokyo

The Graduate University for Advanced Studies (SOKENDAI)

Pascal A. Oesch

University of Geneva

Masami Ouchi

University of Tokyo

Kazuaki Ota

Kyoto University

Ikkoh Shimizu

Osaka University

Yoshiaki Taniguchi

The Open University of Japan

Hideki Umehata

The Open University of Japan


Darach Watson

University of Copenhagen

Publication of the Astronomical Society of Japan

0004-6264 (ISSN)

Vol. 71 4 71

Subject Categories

Astronomy, Astrophysics and Cosmology

Atom and Molecular Physics and Optics

Condensed Matter Physics


Onsala Space Observatory



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