H I studies of the Sculptor group galaxies. V, NGC 253

A study of the H I properties and mass distribution of the Sculptor group galaxy NGC 253, from VLA obserations, is presented. The detected H I disk is fairly small with a diameter of about 0.8 D HO. The rotation curve, derived from the velocity field using a full tilted ring model, is still rising at the last observed point. The maximum observed rotation velocity is 224 km/s at a radius of 8.5 kpc. From this analysis, a systematic velocity of 245 km/s, a mean inclination of 72 deg, and a mean position angle of 229 deg are derived. The study of the mass distribution shows that a two-component (luminous and dark) mass model is needed to explain the observed rotation curve over the whole radius range. (Author)