Feedback from stars and active galactic nuclei is one of the most important processes steering the baryon cycle in galaxies, i.e., the set of complex phenomena driving the interplay between gas, dust, and stars in their interstellar medium (ISM). Such a feedback could be strong enough to produce galactic-scale outflows able to sweep the gas and the dust out of the galaxies, drastically shaping their growth. 

Local dwarf galaxies are ideal candidates to investigate the impact of stellar feedback on galaxy evolution. Indeed, because of their shallow gravitational potential, outflows developed in their ISM could carry gas and dust into the circumgalactic or even intergalactic media (CGM/IGM) more easily than for high-mass sources, substantially affecting their star-formation activity. In addition, they are thought to be analogues of high-redshift sources, opening a window on the study of the primordial Universe.

We found that most of dwarf galaxies host star-formation-driven outflows that , on average, are able to drag  ~40% of the gas outside of the ISM, significantly enriching the surrounding circumgalactic medium, and producing extended atomic gas and dust reservoirs surrounding the galaxies. These results highlight the key role of stellar feedback in the baryon cycle of low-mass sources, and are crucial for calibrating cosmological simulations and analytical models attempting to reproduce the evolution of these galaxies across cosmic time.

Galaxies form converting primordial gas into stars,  but the way they grow their mass is not yet understood. Two main processes have been proposed to efficiently supply fresh gas to galaxies, which are the continuous accretion of gas, and major mergers. Although star formation ignited by gas accretion has been considered as the most efficient mechanism for many years, recent works have suggested a possible increase in the fraction of major mergers at early epochs, reviving the debate on which of the two processes dominates over the other.

I investigated this as part of the ALPINE survey, a 70-hour ALMA large program which obtain sub-mm measurements of the gas and dust content in a hundred of star-forming galaxies emerging from the Epoch of Reionization. ALPINE allowed us to conduct the first panchromatic study of such a large statistical sample of primordial galaxies, and a robust characterization of their morphology and kinematics through the detection of C+ emission line at 158 µm rest-frame.

We found that ~40% of normal galaxies at z~5 was undergoing a merging, a factor of two higher than what measured at the Cosmic Noon from studies based on optical imaging only, These results reveal a significant merging activity in the early Universe, that will be further confirmed by new observations in the rest-frame optical from JWST.

Gas represents the fuel for star formation, which in turn produces new metals and dust that enrich the galaxies' ISM. Notably, dust grains can significantly affect our understanding of galaxy evolution by absorbing the UV light produced by young stars and re-emitting it in the FIR, biasing our measures of the total (UV+FIR) star-formation rate. This is particularly relevant for primordial galaxies, for which the FIR continuum (tracing the dust-obscured star formation) is usually faint (hence, time-consuming) and hard to detect.  

The C+ emission was found to show a tight correlation with the total SFR up to z~2. Being much brighter and easier to detect than the dust continuum, it provides a more direct way to get information on the star-formation activity of distant sources. 

Exploiting data from the ALPINE survey, we have shown that C+ is a very good tracer of star formation up to z~5. Since this line is sensitive to the total SFR and is not affected by the presence of dust, it can even reveal the star formation activity of the most dust-obscured and previously unknown optically-dark sources, allowing us to obtain a complete picture of the cosmic star-formation rate density into the Epoch of Reionization.