Jellyfish galaxies represent the extreme phase of galaxies that, through their infalling into the cluster potential, get stripped of their disc gas leading to an inside-out quenching of their star formation and to the creation of the passive population of galaxies which are dominating the high density regions of the Universe. At odds with expectation, though, the ram pressure stripping responsible for this effect turns out to produce an extremely large amount of cold gas in the disc of the galaxies at their peak-stripping phase, i. e. when they show the longest tails of stripped gas filled with knots of star formation.
This result, hinted by the ALMA data of the optically selected GASP galaxies, has been confirmed by the APEX data of a larger sample of HI selected cluster galaxies, for which we possess MeerKat data.
I will describe the observations that led to this conclusion, and also show that, coupling together all the information on the cold gas content, peak-stripping galaxies are at the same time both HI-poor and H2-rich, following the infall history in the cluster.
This evidence is particularly significant as it is strictly linked to the physics of the gas that leads to the star formation itself in extreme environments (i. e. Compressed disks, but also star forming clumps in the tails), as I will show using ALMA data at ~1 kpc resolution. These findings have therefore a more general impact on our understanding of the star formation process.

Breve CV della Dr. Alessia Moretti:

Alessia Moretti works on galaxy evolution in dense environments as traced by multi-object and IFU spectroscopic data. She has led the data reduction and analysis of the OmegaWINGS spectroscopic data covering wide regions around the WINGS clusters and she is involved in the 4MOST cluster infalling regions project. She is a core team member of the GASP survey aimed at studying the gas removal processes of nearby cluster galaxies. Within GASP she performed the analysis of the molecular gas content of jellyfish galaxies.