Interstellar And Intergalactic Gas Towards Sn-1993j In M-81 - A Study Of Optical And 21-Cm Spectra

We present a study of the interstellar and intergalactic clouds located in the direction of the recent supernova 1993J in M 81 based on the analysis of optical and 21 cm spectra obtained during the first nights after its discovery. The optical spectra were taken at high spectral resolution (FWHM 4 to 6 km s(-1)) using the 4.2 m William Herschel Telescope (La Palma, Spain), covering the resonance lines of CN, Ca II, Ca I, CH+, CH, Na I, Li I and K I. We also observed in Ca II a sample of foreground Galactic stars in the field of the supernova. The 21 cm spectra were taken with the 100 m Effelsberg Radiotelescope (beam FWHM similar or equal to 9') at the position of SN 1993J and in 6 positions around the supernova, at 10' separation.We find numerous absorption lines in the velocity range -139 km s(-1) < v(lsr) < +172 km s(-1), which fall into 3 distinct groups, representing absorption by gas within our Galaxy and its halo, within M 81 itself and in the intergalactic space within the M 81 group of galaxies.The nearby clouds, close to rest velocity, are located at d approximate to 100 pc, beyond a low density region of the local interstellar medium; one of these belongs to the population of high-latitude molecular clouds. In the lower halo of our Galaxy (0.5 kpc less than or similar to d less than or similar to 3 kpc) we find gas at v(lsr) similar or equal to -50 km s(-1) with low depletion, local interstellar abundance and relatively cold temperature; these properties make this cloud a good candidate for cooling gas in a galactic fountain model.In the interstellar gas of M 81 we find two components with properties of cold gas near rest velocity with respect to the rotating disk of that galaxy. We also detect two low density components at -110 km s(-1) and -100 km s(-1) which probably represent gas infalling at moderate velocity onto the disk of M 81. We do not find evidence of neutral gas outflowing from the disk. The group of intergalactic absorptions falls in the range +125 km s(-1) less than or equal to v(lsr) +172 km s(-1). Two of these components show properties of cold, metal-rich gas and are detected in KI and Ca I, the first detections of this type in intergalactic space. The other intergalactic components have low density and originate in warm gas. This complex of gas is most likely the result of a smooth tidal interaction of M 81 with a companion galaxy of its group. Kinematical considerations suggest that the material does not arise from M 81 but probably from M 82. The presence of a stellar component co-existing with such intergalactic structure is consistent with our data.