A large-scale, regular intergalactic magnetic field associated with Stephan's Quintet?

TL;DR

This study presents evidence for a large-scale, regular magnetic field in Stephan's Quintet, potentially the first such structure observed in a galaxy group, with implications for understanding intergalactic magnetism.

Contribution

It provides the first detection and analysis of a large-scale, regular magnetic field associated with a galaxy group, expanding knowledge beyond individual galaxies.

Findings

Detected a large-scale, regular magnetic field in Stephan's Quintet.

Estimated the magnetic field strength to be at least a few microgauss.

The magnetic structure spans at least 60x40x20 kpc, larger than typical galactic fields.

Abstract

Regular magnetic fields are frequently found within and in the outskirts of galaxies, but their presence, properties, and origin has not yet been established for galaxy groups. On the basis of broadband radio polarimetric imaging with the Westerbork Synthesis Radio Telescope (WSRT), we made use of Rotation Measure Synthesis to disentangle contributions from magnetic fields on various scales for several polarised radio sources inside, behind, or in the vicinity of the Stephan's Quintet (HCG92, SQ). We recognise the signature of a large-scale, genuinely regular, magnetised screen, seemingly constrained to the Quintet itself. Although we cannot exclude a contribution from the Milky Way, our analysis favours a magnetic structure within the SQ system. If indeed associated with the galaxy group in question, it would span a volume of at least $60\,\times\,40\,\times\,20\,\mathrm{kpc}$ and have a strength at least as high as that previously detected within large spiral galaxies. This field would then surpass the extent of any other known galactic, regular magnetic fields, have a considerable strength of a few microgauss, and would be the first known example of such a structure in a galaxy system other than a galaxy pair. Several other explanations are also presented and evaluated.