HI STUDIES OF THE SCULPTOR GROUP GALAXIES .5. NGC-253

A study of the H I properties and mass distribution of the Sculptor group galaxy NGC 253, from VLA1 observations, is presented. The detected H I disk is fairly small with a diameter approximately 0.8D(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 V(rot) congruent-to 224 km s-1 at a radius of approximately 8.5 kpc. From this analysis, a systematic velocity of 245 km s-1, a mean inclination i congruent-to 72-degrees, and a mean position angle P. A. congruent-to 229-degrees 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. An exponential disk and an isothermal sphere are fitted to the rotation curve. The maximum (M/L(B))* found is highly dependent on the value of the internal absorption used. It varies from (M/L(B))* congruent-to 4 to (M/L(B))* congruent-to 13 if different absorption corrections are applied to the luminosity profile. The halo parameters are a core radius r(c) congruent-to 27 kpc and a central density rho-o congruent-to 0.015 M. pc-3.