We present a study of the magnetic field properties of NGC 4038/9 ( the ‘ Antennae ’ galaxies ) , the closest example of a late stage merger of two spiral galaxies .
Wideband polarimetric observations were performed using the Karl G. Jansky Very Large Array between 2 and 4 GHz .
Rotation measure synthesis and Faraday depolarization analysis was performed to probe the magnetic field strength and structure at spatial resolution of \sim 1 kpc .
Highly polarized emission from the southern tidal tail is detected with intrinsic fractional polarization close to the theoretical maximum ( 0.62 \pm 0.18 ) , estimated by fitting the Faraday depolarization with a volume that is both synchrotron emitting and Faraday rotating containing random magnetic fields .
Magnetic fields are well aligned along the tidal tail and the Faraday depths shows large-scale smooth variations preserving its sign .
This suggests the field in the plane of the sky to be regular up to \sim 20 kpc , which is the largest detected regular field structure on galactic scales .
The equipartition field strength of \sim 8.5 ~ { } \mu G of the regular field in the tidal tail is reached within a few 100 Myr , likely generated by stretching of the galactic disc field by a factor of 4–9 during the tidal interaction .
The regular field strength is greater than the turbulent fields in the tidal tail .
Our study comprehensively demonstrates , although the magnetic fields within the merging bodies are dominated by strong turbulent magnetic fields of \sim 20 ~ { } \mu G in strength , tidal interactions can produce large-scale regular field structure in the outskirts .