HIGH-RESOLUTION H-I OBSERVATIONS OF THE WHIRLPOOL GALAXY M51

This paper presents new VLA observations in the 21 cm H I line of the Sc spiral galaxy M51 (NGC 5194) at resolutions ranging from 5″ to 34″. The H I in the inner regions follows the spiral structure as outlined by the star-forming regions. In the outer parts of the galaxy faint H I extends to larger radii (up to 21 kpc) and appears to lie in a different plane. From the south a broad H I tail extends even farther and curves to the north and east, over a projected length of 90 kpc. The velocity structure of the gas in M51 is extremely complicated and difficult to interpret. There seems to be a mixture of effects, such as a possible warp and/or oval distortion, streaming motions along the spiral arms, caused by an (interaction-induced?) density wave, and purely tidal tails and bridges. This paper presents the data in various forms and describes some of the most salient features.