GASP: XXVI. HI gas in jellyfish galaxies: The case of JO201 and JO206

We present atomic hydrogen (Hi) observations with the Jansky Very Large Array of one of the jellyfish galaxies in the GAs Stripping Phenomena sample, JO201. This massive galaxy (M = 3:5 1010 M) is falling along the line-of-sight towards the centre of a rich cluster (M200 1:6 1015 M, cl 982 55 km s1) at a high velocity 3363 km s1. Its H emission shows a 40 kpc tail, which is closely confined to its stellar disc and a 100 kpc tail extending further out. We find that Hi emission only coincides with the shorter clumpy H tail, while no Hi emission is detected along the 100 kpc H tail. In total, we measured an Hi mass of MHI = 1:65109 M, which is about 60% lower than expected based on its stellar mass and stellar surface density. We compared JO201 to another jellyfish in the GASP sample, JO206 (of a similar mass but living in a ten times less massive cluster), and we find that they are similarly Hi-deficient. Of the total Hi mass in JO201, about 30% lies outside the galaxy disc in projection. This Hi fraction is probably a lower limit since the velocity distribution shows that most of the Hi is redshifted relative to the stellar disc and could be outside the disc. The global star formation rate (SFR) analysis of JO201 suggests an enhanced star formation for its observed Hi content. The observed SFR would be expected if JO201 had ten times its current Hi mass. The disc is the main contributor of the high star formation effciency at a given Hi gas density for both galaxies, but their tails also show higher star formation effciencies compared to the outer regions of field galaxies. Generally, we find that JO201 and JO206 are similar based on their Hi content, stellar mass, and star formation rate. This finding is unexpected considering their different environments. A toy model comparing the ram pressure of the intracluster medium (ICM) versus the restoring forces of these galaxies suggests that the ram pressure strength exerted on them could be comparable if we consider their 3D orbital velocities and radial distances relative to the clusters.