ALMA witnesses the assembly of first galaxies

Characterising primeval galaxies entails the challenging goal of observing galaxies with modest star formation rates (SFR < 100 M_⊙yr^-1) and approaching the beginning of the reionisation epoch (z > 6). To date a large number of primeval galaxies have been identified thanks to deep near-infrared surveys. However, to further our understanding on the formation and evolution of such primeval objects, we must investigate their nature and physical properties through multi-band spectroscopic observations. Information on dust content, metallicity, interactions with the surrounding environment, and outflows can be obtained with ALMA observations of far-infrared (FIR) lines such as the [C II] at 158 μm and [O III] at 88 μm. Here, we, thus, discuss the recent results unveiled by ALMA observations and present new [C II] observations of BDF-3299, a star-forming galaxy at z = 7.1 showing a spatial and spectral offset between the rest-frame UV and the FIR lines emission.