Enhanced [CII] emission in a z=4.76 submillimetre galaxy

TL;DR

This paper reports the detection of bright [CII] emission in a high-redshift galaxy, revealing insights into its starburst activity, metallicity, and the utility of [CII] as a tracer of interstellar matter at early cosmic times.

Contribution

First detection of [CII] emission in a z=4.76 submillimetre galaxy, highlighting its potential as a reliable tracer of interstellar gas in high-redshift, low-metallicity environments.

Findings

[CII] emission indicates a starburst with high radiation field and density.

High [CII]/FIR and [CII]/CO ratios suggest low metallicity.

[CII] may be more effective than CO in tracing gas at high redshift.

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_0~10^3 and a density ~10^4 cm^-3 in a kpc-scale starburst, as seen in local and high redshift starbursts. The high L_[CII]/L_FIR=2.4x10^-3 and the very high L_[CII]/L_CO(1-0) ~ 10^4 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.