We present ALMA observations of the [ CII ] line and far-infrared ( FIR ) continuum of a normally star-forming galaxy in the reionization epoch , the z = 6.96 Ly \alpha emitter ( LAE ) IOK-1 .
Probing to sensitivities of \sigma _ { line } = 240 \mu Jy beam ^ { -1 } ( 40 km s ^ { -1 } channel ) and \sigma _ { cont } = 21 \mu Jy beam ^ { -1 } , we found the galaxy undetected in both [ CII ] and continuum .
Comparison of 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 3 \sigma FIR continuum limit , corrected for CMB effects , implies intrinsic dust mass M _ { dust } < 6.4 \times 10 ^ { 7 } M _ { \odot } , FIR luminosity L _ { FIR } < 3.7 \times 10 ^ { 10 } L _ { \odot } ( 42.5–122.5 \mu m ) , total IR luminosity L _ { IR } < 5.7 \times 10 ^ { 10 } L _ { \odot } ( 8–1000 \mu m ) and dust-obscured star formation rate ( SFR ) < 10 M _ { \odot } 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 3 \sigma [ CII ] flux limit translates into [ CII ] luminosity , L _ { [ CII ] } < 3.4 \times 10 ^ { 7 } L _ { \odot } .
Locations of IOK-1 and previously observed LAEs on the L _ { [ CII ] } vs. SFR and L _ { [ CII ] } / L _ { FIR } vs . L _ { FIR } 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 .