GASP has provided the first large sample of confirmed ram-pressure stripped galaxies in clusters with a wide range of galaxy masses and cluster masses, in various stages and degrees of stripping. GASP also represents a tremendous step forward in terms of multi-wavelength coverage: this allows to study simultaneously the gas in different phases, the stellar content and the non-thermal processes.
Among the major GASP breakthroughs, there is the characterization of the star formation activity, both in the disks and in the tails. We have been able to study the star-forming regions in the ram pressure stripped disks and tails at a great level of detail. We have obtained the first statistically significant sample of star-forming clumps in the tails of stripped gas, measuring their luminosities, sizes, stellar masses, stellar ages and main scaling relations. We have shown that their masses and stellar mass densities are compatible with them being new dwarf galaxies formed without dark matter. The exquisite spatial resolution of the Hubble Space Telescope images has allowed us to investigate the morphologies of the star forming clumps, confirming the “fireballs effect” by which the remaining ionized gas is confined to the side of the clumps which is further away from the galaxy.
For the first time, we have shown that in jellyfish galaxies the large amount of molecular gas must originate from an efficient conversion of neutral into molecular gas.
Another GASP discovery has been the high incidence of AGN in ram pressure stripped galaxies, highlighting the capability of ram pressure to funnel gas towards the galaxy center.
For the first time, GASP has measured the magnetic field from polarization data in the long stripped tail finding that the magnetic field is well ordered and strongly aligned with the stripping direction. Another unexpected GASP discovery has been that unwinding of spiral arms can be caused by ram pressure stripping. Following up on this, we have published the first catalog of unwinding arm galaxies in low redshift clusters.
Thanks to the large statistics, GASP has also provided the first and only complete census of ram pressure signatures visible from optical imaging in low redshift clusters, showing how common this phenomenon must be among infalling gas-rich galaxies.
GASP has discovered a correlation between the Halpha and the X-ray surface brightness, pointing to the existence of a hot plasma originating from the cooling of the intracluster medium (ICM) or mixing stripped gas-ICM. GASP has observationally measured the gas metallicity scaling relations and metallicity gradients in ram pressure stripped galaxies for the first time and has discovered the imprint of mixing of ICM-stripped gas from the metallicity gradient in stripped tails.
Being the only sufficiently large sample of galaxies in many different galaxy clusters, GASP has been able to characterize the orbits of ram pressure galaxies within clusters and the effects of the cluster dynamical state.
A long standing question has been whether the large population of lenticular galaxies that dominate galaxy clusters today can originate from the quenching of star formation in spiral galaxies. GASP has shown how this is possible and related to ram pressure.
On the simulation side, novel GASP results include the comprehension of the physical processes that push gas towards the center originating the AGN in ram pressure stripped galaxies, and the unexpected result that star formation in the disk does not aid ram pressure stripping nor enhances the rate at which the gas is stripped. GASP hydrodynamical simulations have also shown that the usually employed analytic approximation underpredict the stripping rate of neutral gas and overpredict that of ionized gas.
Finally, we have assessed the success rate of optical imaging in finding ram pressure stripped galaxies, which is important for ongoing and future very large imaging surveys of the sky such as those obtained by Euclid and the Vera Rubin Telescope.
