L'evoluzione delle proprietà dell'HI nelle galassie negli ultimi 8 miliardi di anni

The baryonic mass of galaxies is not only in stars but also in gas, a key driver of galactic evolution. Neutral atomic hydrogen (HI), abundant in halos around disks, both fuels star formation and contributes to its quenching. HI mainly resides in the Cold Neutral Medium, too cool to emit hydrogen’s classical spectral lines. Instead, it is observed via the faint 21-cm spin-flip transition at 1.42 GHz, detectable only through deep radio observations. Because of current sensitivity limits, HI is well mapped only for nearby galaxies, while higher-redshift studies rely on statistical methods such as stacking, where HI spectra or images are co-added to enhance the signal. With a dedicated stacking pipeline, we analyzed star-forming galaxies and derived the MHI–M ⋆ scaling relation at z > 0, a fundamental tool to probe how gas reservoirs evolve, deplete, and connect to stellar growth. While the role of HI in star-forming systems is clear, its presence in passive galaxies remains debated. Applying our method to quiescent samples, we find evidence of a link between HI and dust, suggesting dust regrowth may follow quenching, provided HI survives. Morphology and environment also shape HI abundance, revealing their intertwined influence. We further use the MHI–M ⋆ relation to extend the stellar mass function into an HI mass function (HIMF) at z > 0. Our results show evolution between z = 0 and z = 1, consistent with an increasing HI budget traced by the cosmic HI density (ΩHI). This work provides new constraints on the HI content of galaxies beyond the Local Universe, demonstrating stacking as a powerful probe where direct detections are not yet feasible, and paving the way for breakthroughs with next-generation radio facilities such as the SKA.