Jellyfish galaxies, gas stripping, and X-ray observations: prospects with LEM

Observations across multiple wavelengths have shown that merging galaxies in groups and clusters may exhibit asymmetric distributions of gas and gas tails: these are known as jellyfish galaxies and are evidence of ram-pressure stripping in action. Jellyfish galaxies are thought not only to be affected by their environment, but also to modulate the physical properties of the gas in which they orbit: they deposit cold and warm gas, they bring in metals and they compress their surroundings with large-scale bow shocks due to their high Mach-number speeds. Numerical simulations have been used to study jellyfish galaxies, both in idealized wind-tunnel setups as well as in cosmological galaxy simulations. Among the latter, the cosmological magnetohydrodynamic simulations IllustrisTNG are allowing us to study thousands of jellyfish among tens of thousands of galaxies in groups and clusters ranging three orders of magnitude in total halo mass. This vast dataset joint with catalogs from other numerical codes will be used to study the prospects of the Line Emission Mapper (LEM) to constrain ram-pressure stripping and the mixing of the tail gas with the surrounding intra-group and intra-cluster medium. LEM is a proposal for a NASA probe-class mission and, thanks to its spectral resolution, it will allow us to separate the signal of the cooler gas stripped from jellyfish galaxies, whose emission is dominated by soft X-ray lines, from the hotter medium of the host halo. This in turn will allow us to get insight into, and to make more direct connections to theoretical expectations for, the heating, cooling and ionization processes in the tail and at the tail-medium interface, the time scales of metal mixing, shocks, the properties of the ambient plasma, including magnetic fields, and the multi-phase nature of the tail gas in comparison to the interstellar medium in normal galaxies.