Abstract
Ram-pressure stripping is a crucial evolutionary driver for cluster galaxies and jellyfish galaxies characterized by very extended tails of stripped gas, and they are the most striking examples of it in action. Recently, those extended tails are found to show ongoing star formation, raising the question of how the stripped, cold gas can survive long enough to form new stars outside the stellar disk. In this study, we summarize the most recent results achieved within the GASP collaboration to provide a holistic explanation for this phenomenon. We focus on two textbook examples of jellyfish galaxies, JO206 and JW100, for which, via multi-wavelength observations from radio to X-ray and numerical simulations, we have explored the different gas phases (neutral, molecular, diffuse-ionized, and hot). Based on additional multi-phase gas studies, we now propose a scenario of stripped tail evolution including all phases that are driven by a magnetic draping sheath, where the intracluster turbulent magnetized plasma condenses onto the galaxy disk and tail and produces a magnetized interface that protects the stripped galaxy tail gas from evaporation. In such a scenario, the accreted environmental plasma can cool down and eventually join the tail gas, hence providing additional gas to form stars. The implications of our findings can shed light on the more general scenario of draping, condensation, and cooling of hot gas surrounding cold clouds that is fundamental in many astrophysical phenomena.
Highlights
On cosmic scales, star formation activity in galaxies has strongly declined since z∼2 such that a large number of galaxies have evolved into passive galaxies while the star formation rate at fixed stellar mass has decreased [1]
We provide a summary of the recent results collected within the GASP collaboration including the analysis of the cold neutral and molecular gas, diffuse ionized gas tracers, hot gas, radio continuum, and linear polarization
Both the diverse observations and recent simulations of a gas cloud facing a turbulent, hot, and magnetized ICM wind agree with a scenario in which the galaxy accretes hot plasma forming a magnetic draping layer at the leading edges and further along the tail preventing the stripped tail gas from evaporation while the ICM plasma becomes mixed with ISM and cools from the outside-in
Summary
Star formation activity in galaxies has strongly declined since z∼2 such that a large number of galaxies have evolved into passive galaxies while the star formation rate at fixed stellar mass has decreased [1]. By measuring radio continuum brightness and spectral index trend in direction of the galaxy tail, these works found an excess in radio emission that cannot be explained by the current star formation in the Hα emitting knots This can be the result of the ram-pressure stripping process in agreement with the steepening of the spectral index with distance to the galaxy disks, which is expected in a scenario where electrons travel from the disk to the tail and release their energy, indicating standard electron cooling. Based on the LoTSS observations, [27,28] reported the discovery of hundreds of radio jellyfish in lowz clusters and groups These results indicate that the formation of radio tails is ubiquitous in clusters and showed that LOFAR can be a powerful instrument for identifying ram pressure stripped galaxies across extremely wide fields
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