Star-forming clumps in jellyfish galaxy tails

Star-forming, Halpha-emitting clumps are found in the tails of galaxies undergoing intense ram-pressure stripping in galaxy clusters (so-called jellyfish galaxies). These clumps offer a unique opportunity to study the star formation process under extreme conditions, in the absence of an underlying disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution study of these systems is missing. We propose to observe the first statistical sample of clumps in the tails (250) and disks (500) of six jellyfish galaxies, using a combination of broad-band filters (UV- to I) and a narrow-band Halpha filter. HST observations are needed to study the sizes, stellar masses and ages of the clumps and their clustering hierarchy, investigating whether the hierarchical structure in the tails follows the one in disks. We will study the clump scaling relations, explore the universality of the star formation process and verify whether a disk is irrelevant for star formation, as hinted by jellyfish galaxy results so far. We will investigate the nature and fate of these clumps, as well as the nature of the diffuse emission in the tails where smaller, so far undetected clumps might exist. The unmatched spatial resolution of HST (70pc in our case) will create a powerful synergy with available multi-wavelength data at lower (1kpc) resolution (MUSE, ALMA, JVLA). This program is the first HST systematic study of jellyfish galaxies at low-z. A relatively modest investment of HST will lead to a breakthrough in understanding the connection between ram pressure stripping and star formation, as well as the mechanisms regulating the star formation process in general.