Enhanced [CII] emission in az = 4.76 submillimetre galaxy

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Abstract
We present the detection of bright [CII] emission in the z = 4.76 submillimetre galaxy LESS J033229.4-275619 using the Atacama Pathfinder EXperiment. This represents the highest redshift [CII] detection in a submm selected, star-formation dominated system. The AGN contributions to the [CII] and far-infrared (FIR) luminosities are small. We find an atomic mass derived from [CII] comparable to the molecular mass derived from CO. The ratio of the [CII], CO and FIR luminosities imply a radiation field strength G 0 ~ 103 and a density ~ 104 cm-3 in a kpc-scale starburst, as seen in local and high redshift starbursts. The high L [CII] /L FIR = 2.4 × 10-3 and the very high L [CII] /L CO(1 − 0) ≈ 104 are reminiscent of low metallicity dwarf galaxies, suggesting that the highest redshift star-forming galaxies may also be characterised by lower metallicities. We discuss the implications of a reduced metallicity on studies of the gas reservoirs, and conclude that especially at very high redshift, [CII] may be a more powerful and reliable tracer of the interstellar matter than CO.
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