Interstellar and intergalactic gas in the direction of SN 1993J in M 81

During the first few nights following its discovery, we observed the interstellar Ca II and Na I lines towards supernova 1993J at high spectral resolution (FWHM ∼ 5-6 km s −1 ) with the William Herschel Telescope at La Palma. We find a crowd of absorption components in the radial-velocity range −135 km s −1 < υ lsr < +165 km s −1 . In order to understand the origin of these features, we re-examined previous surveys of local interstellar gas, high-velocity gas, and intergalactic gas in the field. We also observed the line of sight of the supernova at 21 cm with the 100-m Radiotelescope of Effelsberg. We find that the components between +85 and +165 km s −1 originate in intergalactic gas within the M81 group of galaxies, tidally pulled out from one of the galaxies of the group