Messier 81's Planck view versus its halo mapping

This paper is a follow-up of a previous paper about the M 82 galaxy and its halo based on Planck observations. As in the case of M 82, a substantial north-south and east-west temperature asymmetry is also found for the M 81 galaxy, extending up to galactocentric distances of about 1.5°. The temperature asymmetry is almost frequency independent and can be interpreted as a Doppler-induced effect related to the M 81 halo rotation and/or triggered by the gravitational interaction of the galaxies within the M 81 Group. Along with the analogous study of several nearby edge-on spiral galaxies, the cosmic microwave background temperature asymmetry method thus is shown to act as a direct tool to map the galactic haloes and/or the intergalactic bridges, invisible in other bands or by other methods.