Extragalactic magnetism with SOFIA (SALSA Legacy Program). VI. The magnetic fields in the multi-phase interstellar medium of the Antennae galaxies

Abstract

Mergers are thought to be a fundamental channel for galaxy growth, perturbing the gas dynamics and the magnetic fields (B-fields) in the interstellar medium (ISM). However, the mechanisms that amplify and dissipate B-fields during a merger remain unclear. We characterize the morphology of the ordered B-fields in the multi-phase ISM of the closest merger of two spiral galaxies, the Antennae galaxies. We compare the inferred B-fields using $154\mu$m thermal dust and $11$ cm radio synchrotron emission polarimetric observations. We find that the $154\mu$m B-fields are more ordered across the Antennae galaxies than the $11$ cm B-fields. The turbulent-to-ordered $154\mu$m B-field increases at the galaxy cores and star-forming regions. The relic spiral arm has an ordered spiral $154\mu$m B-field, while the $11$ cm B-field is radial. The $154\mu$m B-field may be dominated by turbulent dynamos with high ${}^{12}$CO(1-0) velocity dispersion driven by star-forming regions, while the $11$ cm B-field is cospatial with high HI velocity dispersion driven by galaxy interaction. This result shows the dissociation between the warm gas mainly disturbed by the merger, and the dense gas still following the dynamics of the relic spiral arm. We find a $\sim 8.9$ kpc scale ordered B-field connecting the two galaxies. The base of the tidal tail is cospatial with the HI and ${}^{12}$CO(1-0) emission and has compressed and/or sheared $154\mu$m and $11$ cm B-fields driven by the merger. We suggest that amplify B-fields, with respect to the rest of the system and other spiral galaxies, may be supporting the gas flow between both galaxies and the tidal tail.

11 pages, 5 figures, Accepted for publication in ApJ Letters

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