A wide-field HI mosaic of Messier 31. II.The disk warp, rotation and the dark matter halo

Understand

We test cosmological models of structure formation using the rotation curve of the nearest spiral galaxy, M31, determined using a recent deep, full-disk 21-cm imaging survey smoothed to 466 pc resolution.

• We fit a tilted ring model to the HI data from 8 to 37 kpc.
• The disk of M31 warps from 25 kpc outwards and becomes more inclined with respect to our line of sight.
• Newtonian dynamics without a dark matter halo provide a very poor fit to the rotation curve derived using the warp model.