Highly ordered magnetic fields in the tail of the jellyfish galaxy JO206

Abstract

Jellyfish galaxies have long tails of gas that is stripped from the disk by ram pressure due to the motion of galaxies in the intracluster medium in galaxy clusters. Here, we present the magnetic field strength and orientation within the disk and the (90-kpc-long) Hα-emitting tail of the jellyfish galaxy JO206. The tail has a large-scale magnetic field (>4.1 μG), a steep radio spectral index (α ≈ -2.0), indicating an ageing of the electrons propagating away from the star-forming regions, and extremely high fractional polarization (>50 %), indicating low turbulent motions. The magnetic field vectors are aligned with (parallel to) the direction of the ionized-gas tail and stripping direction. High-resolution simulations of a large, cold gas cloud that is exposed to a hot, magnetized turbulent wind show that the fractional polarization and ordered magnetic field can be explained by accretion of draped magnetized plasma from the hot wind that condenses onto the external layers of the tail, where it is adiabatically compressed and sheared. The ordered magnetic field, preventing heat and momentum exchange, may be a key factor in allowing in situ star formation in the tail.