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Characterizing the primeval galaxies of the Universe entails the challenging goal of observing galaxies with modest star formation rates (< 100 Msun/yr) 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 IR 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 FIR fine structure lines such as the [CII] at 158 um and [OIII] at 88 um. ALMA observations reveal that the [OIII] and [CII] emission in z$>$5 star-forming galaxies are partly clumpy and partly diffuse on scales larger than 1kpc. Our analysis reveal that 9 out of 21 galaxies having ALMA [CII] detection break into multiple components and only a fraction of which, if any, are associated with the primary rest-frame UV components, while the bulk of the [CII] emission is associated with fainter rest-frame UV components, or not associated with any UV counterparts at the current limits at all. By taking into account the presence of all these sub-components, we found that the L[CII]-SFR relation in the early epoch has a dispersion two times larger than that observed in the local population. This dispersion reflects the heterogeneous properties of the primeval galaxies. We find that the [CII] luminosity is lower in high Lyα equivalent width (EW) sources than those with high Lyα EW, suggesting that the metallicity plays an important role on the [CII] emission as also expected by recent simulations. The angular resolution of ALMA observations has also allow us to investigate the relation between [CII] surface brightness and star formation rate density. Finally we discuss that the complex properties revealed by ALMA in z>5 galaxies are consistent with expectations by recent models and cosmological simulations, in which differential dust extinction, differential excitation and different metal enrichment levels, associated with different subsystems assembling a galaxy, are responsible for the various appearance of the system when observed with distinct tracers.

I present an overview of our results from the MAGNUM survey (Measuring Active Galactic Nuclei Under MUSE Microscope), which aims at studying in detail the properties of AGN, including their interaction with the host galaxy (e.g., tentative evidence of “positive feedback”), and the ISM gas properties, both in the ionised gas with VLT/MUSE and in the molecular gas with ALMA. Nearby galaxies are the ideal laboratories for such a detailed analysis, thanks to the spatial information offered by their vicinity (the average spatial resolution is ~50 pc). Data have been obtained for ten local galaxies so far, including the famous NGC 1068, Circinus and NGC 4945. Thanks to its unique combination of large field of view (1’x1’) and spectral coverage (4800−9300 Å), MUSE has allowed us to probe the kinematical and spatial structure of the kpc-scale AGN-driven outflows, to construct spatially resolved BPT diagrams to spatially disentangle the main ionisation mechanism and constrain the physical properties of the ISM (reddening, density, temperature, ionisation potential, shock excitation etc). The intrinsic outflow 3D shape and the physical properties of the gas can then be analysed in details through kinematical and photoionisation models.