Alma observation of 158μm [Cii] line and dust continuum of a z = 7 normally star-forming galaxy in the epoch of reionization

Kazuaki Ota, Fabian Walter, Kouji Ohta, Bunyo Hatsukade, Chris L. Carilli, Elisabete Da Cunha, Jorge González-López, Roberto Decarli, Jacqueline A. Hodge, Hiroshi Nagai, Eiichi Egami, Linhua Jiang, Masanori Iye, Nobunari Kashikawa, Dominik A. Riechers, Frank Bertoldi, Pierre Cox, Roberto Neri, Axel Weiss

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86 Scopus citations


We present ALMA observations of the [C II] line and far-infrared (FIR) continuum of a normally star-forming galaxy in the reionization epoch, the z = 6.96 Lyα emitter (LAE) IOK-1. Probing to sensitivities of σline = 240 μJy beam-1 (40 km s-1 channel) and σcont = 21 μJy beam-1, we found the galaxy undetected in both [C II] and continuum. Comparison of ultraviolet (UV)-FIR spectral energy distribution (SED) of IOK-1, including our ALMA limit, with those of several types of local galaxies (including the effects of the cosmic microwave background, CMB, on the FIR continuum) suggests that IOK-1 is similar to local dwarf/irregular galaxies in SED shape rather than highly dusty/obscured galaxies. Moreover, our 3σ FIR continuum limit, corrected for CMB effects, implies intrinsic dust mass Mdust < 6.4 × 107 M, FIR luminosity LFIR < 3.7 × 1010 L (42.5-122.5 μm), total IR luminosity LIR < 5.7 × 1010 L (8-1000 μm), and dust-obscured star formation rate (SFR) < 10 M yr-1, if we assume that IOK-1 has a dust temperature and emissivity index typical of local dwarf galaxies. This SFR is 2.4 times lower than one estimated from the UV continuum, suggesting that <29% of the star formation is obscured by dust. Meanwhile, our 3σ [C II] flux limit translates into [C II] luminosity, L[C II] < 3.4 × 107 L. Locations of IOK-1 and previously observed LAEs on the L[C II] versus SFR and L [C II]/LFIR versus LFIR diagrams imply that LAEs in the reionization epoch have significantly lower gas and dust enrichment than AGN-powered systems and starbursts at similar/lower redshifts, as well as local star-forming galaxies.

Original languageEnglish (US)
Article number34
JournalAstrophysical Journal
Issue number1
StatePublished - Sep 1 2014


  • cosmology: observations
  • early universe
  • galaxies: evolution
  • galaxies: formation

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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