Context : Magnetic fields are essential to fully understand the interstellar medium ( ISM ) and its role in the disk-halo interface of galaxies is still poorly understood .
Star formation is known to expel hot gas vertically into the halo and these outflows have important consequences for mean-field dynamo theory in that they can be efficient in removing magnetic helicity .

Aims : We aim to probe the vertical magnetic field and enhance our understanding of the disk-halo interaction of galaxies .
Studying a face-on galaxy is essential so that the magnetic field components can be separated in 3D .

Methods : We perform new observations of the nearby face-on spiral galaxy NGC 628 with the Karl G. Jansky Very Large Array ( JVLA ) at S-band ( 2.6–3.6 GHz effective bandwidth ) and the Effelsberg 100-m telescope at frequencies of 2.6 GHz and 8.35 GHz with a bandwidth of 80 MHz and 1.1 GHz , respectively .
Owing to the large bandwidth of the JVLA receiving system , we obtain some of the most sensitive radio continuum images in both total and linearly polarised intensity of any external galaxy observed so far .

Results : The application of RM Synthesis to the interferometric polarisation data over this large bandwidth provides high-quality images of Faraday depth and polarisation angle from which we obtained evidence for drivers of magnetic turbulence in the disk-halo connection .
Such drivers include a superbubble detected via a significant Faraday depth gradient coinciding with a { H \scriptstyle I } hole .
We observe an azimuthal periodic pattern in Faraday depth with a pattern wavelength of 3.7 \pm 0.1 kpc , indicating Parker instabilities .
The lack of a significant anti-correlation between Faraday depth and magnetic pitch angle indicates that these loops are vertical in nature with little helical twisting , unlike in IC 342 .
We find that the magnetic pitch angle is systematically larger than the morphological pitch angle of the polarisation arms which gives evidence for the action of a large-scale dynamo where the regular magnetic field is not coupled to the gas flow and obtains a significant radial component .
We additionally discover a lone region of ordered magnetic field to the north of the galaxy with a high degree of polarisation and a small pitch angle , a feature that has not been observed in any other galaxy so far and is possibly caused by an asymmetric { H \scriptstyle I } hole .

Conclusions : Until now NGC 628 has been relatively unexplored in radio continuum but with its extended { H \scriptstyle I } disk and lack of active star formation in its central region has produced a wealth of interesting magnetic phenomena .
We observe evidence for two drivers of magnetic turbulence in the disk-halo connection of NGC 628 , namely , Parker instabilities and superbubbles .