HIGH-RESOLUTION OBSERVATIONS OF NEUTRAL HYDROGEN IN M31-II - VELOCITY-FIELD

The radial velocity of the neutral atomic hydrogen in M31 has been observed with a beam 300 × 1800 pc in the plane of the galaxy. Large-scale features of the observations are in good agreement with previous H I observations, but the interpretation in terms of M/L ratios in the outer parts of M31 differs from that suggested by Roberts & Whitehurst. There are velocity perturbations associated with H I arms which can be explained in terms of the selfgravity of the gas without invoking the density-wave theory of spiral structure. H I with anomalous velocities within 7′ of the nucleus is described. Very close agreement between H I and H II velocities is found. © 1976 Royal Astronomical Society.