  In several spiral galaxies that are observed face-on, large-scale ordered
magnetic fields (the so-called magnetic arms) were found. One of the
explanations was the action of the magnetic reconnection, which leads to a
higher ordering of the magnetic fields. Because it simultaneously converts the
energy of the magnetic fields into thermal energy of the surroundings, magnetic
reconnection has been considered as a heating mechanism of the interstellar
medium for many years. Until recently, no clear observational evidence for this
phenomenon was found. We search for possible signatures of gas heating by
magnetic reconnection effects in the radio and X-ray data for the face-on
spiral galaxy NGC628 (M74), which presents pronounced magnetic arms and
evidence for vertical magnetic fields. The strengths and energy densities of
the magnetic field in the spiral and magnetic arms were derived, as were the
temperatures and thermal energy densities of the hot gas, for the disk and halo
emission. In the regions of magnetic arms, higher order and lower energy
density of the magnetic field is found than in the stellar spiral arms. The
global temperature of the hot gas is roughly constant throughout the disk. The
comparison of the findings with those obtained for the starburst galaxy M83
suggests that magnetic reconnection heating may be present in the halo of
NGC628. The joint analysis of the properties of the magnetic fields and the hot
gas in NGC628 also provided clues for possible tidal interaction with the
companion galaxy.
