1995A&A...295..289E

X-ray observations of M51 and its companion using the ROSAT High Resolution Imager (HRI) reveal diffuse and point-like X-ray emission from both galaxies with (0.1-2.4keV) X-ray luminosities L_x=4.4x10⁴⁰erg/s and 0.7x10⁴⁰erg/s, respectively. Eight point sources are detected in M51 superimposed onto the diffuse emission of the galactic halo. The nuclear area of M51 is a bright extended X-ray source due to hot, outflowing gas coincident with the radio emission of the jet and the southern extranuclear cloud. The companion, NGC 5195, also shows extended emission and at least one other point-like source. NGC 5195 is connected to M51 by a bridge of diffuse X-ray emission. The extents of the diffuse, weak X-ray emission and of the radio continuum emission are comparable. The scale lengths of the thermal radio continuum emission and of the diffuse X-ray emission are similar, favoring the idea that both emission processes are connected to star formation. If the energy densities of magnetic fields and hot gas with a volume filling factor η in the halo of M51 are comparable, then we find from an electron density of 2.6x10^–3η^–1/2cm^–3 a reasonable magnetic field strength of 6.3η^–1/4µG. Some peaks of diffuse X-ray emission coincide with regions of anomalous Faraday depolarization in radio continuum, indicating that the distribution of the hot gas is influenced by magnetic fields. A hot halo may contribute to the depolarization.