GASP. IX. Jellyfish galaxies in phase-space: an orbital study of intense ram-pressure stripping in clusters

Abstract

It is well known that galaxies falling into clusters can experience gas\nstripping due to ram-pressure by the intra-cluster medium (ICM). The most\nspectacular examples are galaxies with extended tails of optically-bright\nstripped material known as "jellyfish". We use the first large homogeneous\ncompilation of jellyfish galaxies in clusters from the WINGS and OmegaWINGS\nsurveys, and follow-up MUSE observations from the GASP MUSE programme to\ninvestigate the orbital histories of jellyfish galaxies in clusters and\nreconstruct their stripping history through position vs. velocity phase- space\ndiagrams. We construct analytic models to define the regions in phase-space\nwhere ram-pressure stripping is at play. We then study the distribution of\ncluster galaxies in phase-space and find that jellyfish galaxies have on\naverage higher peculiar velocities (and higher cluster velocity dispersion)\nthan the overall population of cluster galaxies at all clustercentric radii,\nwhich is indicative of recent infall into the cluster and radial orbits. In\nparticular, the jellyfish galaxies with the longest gas tails reside very near\nthe cluster cores (in projection) and are moving at very high speeds, which\ncoincides with the conditions of the most intense ram-pressure. We conclude\nthat many of the jellyfish galaxies seen in clusters likely formed via fast\n(~1- 2 Gyr), incremental, outside-in ram-pressure stripping during first infall\ninto the cluster in highly radial orbits.\n