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


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.

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Fig. 1: Total intensity results of the 2.7 GHz data.
Fig. 2: Polarization results of the 2.7 GHz data.
Fig. 3: Large-scale alignment of the magnetic field vectors along the galaxy tail derived from the polarization angle.
Fig. 4: Initial time evolution of magnetic field components, B, the vertical velocity, vy, and the gas density, n, in the simulation with a turbulent wind.
Fig. 5: Simulated mock synchrotron observables of a cold (T = 104 K) gas cloud that interacts with a supersonic ICM at four cloud crushing timescales.
Fig. 6: Slices of the temperature distribution overlaid with magnetic field vectors at four cloud crushing timescales.

Data availability

The datasets generated and/or analysed during the current study are available from the corresponding author on reasonable request. The JVLA 1.4 GHz data are available in the National Radio Astronomy Observatory (NRAO) archive (https://science.nrao.edu/facilities/vla/archive/index) and can be found via the project numbers stated in the Methods. At the end of this year, the 2.7 GHz data will also be available in the NRAO archive and can also be found via the project numbers stated in the Methods.

Code availability

The code used during data preparation and analysis is public and available from the corresponding author on reasonable request. The Arepo code, which was used for the present simulations, is also publicly available64.


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This work is based on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere under ESO programme 196.B-0578. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreements 833824 and 679627). We acknowledge funding from the INAF mainstream funding programme (principal investigator B.V.) and from the agreement ASI-INAF n.2017-14-H.0. B.V. acknowledges the Italian PRIN-Miur 2017 (principal investigator A. Cimatti). C.P. acknowledges support by the ERC under ERC-CoG grant CRAGSMAN-646955.

Author information




A. Müller carried out the imaging and analysis of the 2.7 GHz data as well as its interpretation, contributed to the comparison of the radio and optical data, and coordinated the research. B.P. provided the data from the Multi Unit Spectroscopic Explorer (MUSE), an integral field spectrograph, used in this paper and the measurements of the SFRD, contributed to the comparison of the radio and optical data and its interpretation. A. Müller, B.P. and C.P. contributed to the text of the manuscript. C.P. contributed to the various magnetic field estimates and M.S. ran the simulations; M.S. and C.P. contributed to the analysis code, the synchrotron modelling and the interpretation of the simulations. P.S. carried out the 1.4 GHz data reduction and contributed to the interpretation of the results. B.A. contributed to the 2.7 GHz data reduction and its interpretation. A.I. and M.G. carried out the analysis of the archival Chandra X-ray observation to asses the thermal properties of the cluster. R.-J.D. contributed to the scientific discussion. B.V. and A. Moretti contributed to the MUSE data acquisition and analysis, and the interpretation of the results.

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Correspondence to Ancla Müller.

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Peer review information Nature Astronomy thanks Rüdiger Pakmor and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Information

Supplementary Figs. 1–7, Results and Discussion, and Tables 1–3.

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Müller, A., Poggianti, B.M., Pfrommer, C. et al. Highly ordered magnetic fields in the tail of the jellyfish galaxy JO206. Nat Astron (2020). https://doi.org/10.1038/s41550-020-01234-7

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