Extending the HI rotation curve of Messier 31

¹ Département de Physique and Observatoire du Mont Mégantic, Université de Montréal, CP 6128, Succ. Centre-Ville, Montréal, Qc, Canada, H3C 3J7
² Observatoire de Paris, Section Meudon, GEPI, CNRS-UMR 8111 & Université Paris 7, 5 Pl. Janssen, 92195 Meudon, France
³ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

Abstract

New 21-cm observations of Messier 31 are used to measure its rotation curve up to a radius of ~40 kpc. The observations were obtained at the Effelsberg 100-m telescope and extend by ~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 ~1 for a total mass of ~4.5 × 10¹¹ M_๏, 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 Hα emission line.