  Studies of nearby spiral galaxies in radio and X-ray wavelengths reveal the
structure and energy balance of the magnetic fields and the hot interstellar
medium (ISM). In some spiral galaxies, large-scale ordered magnetic fields have
been found between the spiral stellar arms (the so-called magnetic arms). One
of the considered explanations of their origin is magnetic reconnection, which
according to theoretical studies can efficiently heat the low-density ISM. We
present, for the first time, high-resolution C-band (5GHz) radio maps of the
nearby face-on spiral galaxy M101 to study the magnetic fields and verify the
existence of the magnetic arms. The analysis of the archival XMM-Newton X-ray
data is performed to search for signatures of gas heating by magnetic
reconnection effects in the disk and the halo of this galaxy. We combine the
Very Large Array (VLA) and Effelsberg radio maps of M101 to restore the
large-scale emission lost in the interferometric observations. From the
obtained maps, we derive magnetic field strengths and energy densities, and
compare them with the properties of the hot gas found with the spectral
analysis of the X-ray data. Most of the X-ray emission likely comes from the
hot gas in the halo of M101. Its temperature is highest above the massive
stellar arm and an inter-arm region with enhanced polarised radio emission, as
well as in the inter-arm area where neither Halpha nor HI emission is visible.
In regions outside of the spiral arms lower strengths, energy densities and
higher orders of the magnetic fields were observed. Although M101 does not
possess well-defined magnetic arms, a rudimentary magnetic arm was identified
in one of the inter-arm regions. We found weak signatures of additional heating
of the ISM there, as well as in the galactic halo, which could be explained by
the action of magnetic reconnection.
