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We present the results of a Very Large Array H i imaging survey aimed at understanding why some galaxies develop long extraplanar H α tails, becoming extreme jellyfish galaxies. The observations are centered on five extreme jellyfish galaxies optically selected from the WINGS and OMEGAWINGS surveys and confirmed to have long H α tails through MUSE observations. Each galaxy is located in a different cluster. In the observations, there are in total 88 other spiral galaxies within the field of view (40′ Ă— 40′) and observed bandwidth (6500 km sâˆ'1). We detect 13 of these 88 spirals, plus one uncataloged spiral, with H i masses ranging from 1 to 7 Ă— 109 M ⊙. Many of these detections have extended H i disks, two show direct evidence for ram pressure stripping, and others are possibly affected by tidal forces and/or ram pressure stripping. We stack the 75 nondetected spiral galaxies and find an average H i mass of 1.9 Ă— 108 M ⊙, which, given their average stellar mass, implies that they are very H i deficient. Comparing the extreme jellyfish galaxies to the other disk galaxies, we find that they are at smaller projected distance from the cluster center, and have a higher stellar mass and higher relative velocity than all other H i detections and most nondetections. We conclude that the high stellar mass allows extreme jellyfish galaxies to fall deeply into the cluster before being stripped, and the surrounding ICM pressure gives rise to their spectacular star-forming tails. [ABSTRACT FROM AUTHOR]

We present VLA H  i observations of JO206, a prototypical ram-pressure-stripped galaxy in the GASP sample. This massive galaxy (M * = 8.5 × 1010 M⊙) is located at a redshift of z  = 0.0513, near the centre of the low-mass galaxy cluster, IIZw108 (σ ∼ 575  km s−1). JO206 is characterized by a long tail (≥90 kpc) of ionized gas stripped away by ram pressure. We find a similarly long H  i tail in the same direction as the ionized gas tail and measure a total H  i mass of 3.2 × 109 M⊙. This is about half the expected H  i mass given the stellar mass and surface density of JO206. A total of 1.8 × 109 M⊙ (60 per cent) of the detected H  i is in the gas-stripped tail. An analysis of the star formation rate shows that the galaxy is forming more stars compared to galaxies with the same stellar and H  i mass. On average we find an H  i gas depletion time of ∼0.5 Gyr which is about four times shorter than that of 'normal' spiral galaxies. We performed a spatially resolved analysis of the relation between star formation rate density and gas density in the disc and tail of the galaxy at the resolution of our H  i data. The star formation efficiency of the disc is about 10 times higher than that of the tail at fixed H  i surface densities. Both the inner and outer parts of JO206 show an enhanced star formation compared to regions of similar H  i surface density in field galaxies. The enhanced star formation is due to ram-pressure stripping during the galaxy's first infall into the cluster. [ABSTRACT FROM AUTHOR]