Abstract

New 21-cm observations of Messier 31 are used to measure its rotation curve up to a radius of similar to 40 kpc. The observations were obtained at the Effelsberg 100-m telescope and extend by similar to 15 kpc the radius of the last measured point of the rotation curve. A preliminary model of the mass distribution shows that at the last observed velocity point, the dark-to-luminous mass ratio is similar to 1 for a total mass of similar to 4.5 x 1011 M(D, which value is comparable with that of the Milky Way. This exploratory project is ongoing and other Hi observations using other radio-telescopes are planned to confirm this result, as well as a mosaic of the Ha emission line.