Astrophys. J., 792, 34 (2014/September-1)
ALMA observation of 158 µm [C II] line and dust continuum of a z = 7 normally star-forming galaxy in the epoch of reionization.
OTA K., WALTER F., OHTA K., HATSUKADE B., CARILLI C.L., DA CUNHA E., GONZALEZ-LOPEZ J., DECARLI R., HODGE J.A., NAGAI H., EGAMI E., JIANG L., IYE M., KASHIKAWA N., RIECHERS D.A., BERTOLDI F., COX P., NERI R. and WEISS A.
Abstract (from CDS):
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 (40 km/s channel) and σcont= 21 µJy/beam, 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< 6.4x107 M☉, FIR luminosity LFIR< 3.7x1010 L☉(42.5-122.5 µm), total IR luminosity LIR< 5.7x1010 L☉(8-1000 µm), and dust-obscured star formation rate (SFR) < 10 M☉/yr, 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]_< 3.4x107 L☉. Locations of IOK-1 and previously observed LAEs on the L_[C II]_ versus SFR and L_[C II]/LFIR_versus LFIRdiagrams 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.
cosmology: observations - early universe - galaxies: evolution - galaxies: formation
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