Vol. 586
In section 1. Letters

An ALMA view of the interstellar medium of the z=4.77 lensed starburst SPT-S J213242-5802.9

Gravitational lensing is a useful tool for amplifying high-redshift galaxies, such as this SPT2132-58 source at z=4.77, which was studied with ALMA and is amplified by a factor ~6. The NII, CII, CI, and CO lines detected in this source reveal an intense starburst, a HyLIRG (SFR=1120 Msun/yr) with a relatively modest gas reservoir (3.8 10^10Msun), and a very short gas depletion timescale (34 Myr). The interstellar medium is highly excited, as shown by the CO(12-11) line, and it suggests the presence of an AGN. The [CII]/[NII] ratio (26) is the highest one found in a high-redshift galaxy and indicates a chemically-evolved medium (metallicity between 0.5 and 1.5 solar). This source is an important laboratory to understand the extremely quick stellar mass assembly of the first massive galaxies.