Messier 81's Planck view vs its halo mapping
  This paper is a follow-up of a previous paper about the M82 galaxy and its
halo based on Planck observations. As in the case of M82, so also for the M81
galaxy a substantial North-South and East-West temperature asymmetry is found,
extending up to galactocentric distances of about $1.5^\circ$. The temperature
asymmetry is almost frequency independent and can be interpreted as a
Doppler-induced effect related to the M81 halo rotation and/or triggered by the
gravitational interaction of the galaxies within the M81 Group. Along with the
analogous study of several nearby edge-on spiral galaxies, the CMB 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.
