Revealing the onset of star-formation by studying high-redshift clumpy galaxies with ALMA

Star-forming galaxies at z ~ 2 - 4 seem to be more gas-rich than local galaxies and to have gravitationally-unstable interstellar medium. Simulations predict that such conditions allow the formation of massive star-forming regions, dubbed "clumps", 100 times larger and more massive than local star-forming regions. While clumps have been extensively studied at UV and optical wavelengths, their molecular gas and dust reservoirs have hardly been observed and are still poorly constrained. We tackled these open questions by investigating the [CII] and dust morphology of a z ~ 3.4 lensed galaxy hosting four clumps detected in the UV continuum. We conducted ALMA observations probing scales down to ∼ 300 pc and detected three [C II] clumps, while we do not detect the dust continuum. We used the [CII] luminosity as a tracer of molecular gas, as recently suggested by severeal observational and theoretical studies, to estimate the star formation efficiency of clumps and investigate their location in the Schmidt-Kennicutt plane. This revealed that clumps span a range of SFE, likely depending on their evolutionary phase (early formation vs more evolved ages). These observations suggest that multi-wavelength observations ranging from the UV to the FIR are key to understand the onset of star formation and the role of clumps in galaxy evolution. I will conclude the presentation by discussing future prospects and developments.