Can someone give me a reference which gives the rotation curve of the Andromeda galaxy (as well as its radius)?
See Figs. 6 and 7 of Wide-field HI mosaic of Messier 31 II. The disk warp, rotation and the dark matter halo.
Starting from the center, rotational velocity increases to a local maximum of about 250 km/s at 14 kpc, decreases somewhat to a local minumum of 220 km/s at 25 kpc, and final rises to a maximum of about 260 km/s by 40 kpc.
See also Fig. 11 of HI KINEMATICS AND DYNAMICS OF MESSIER 31 which plots rotational curves from four studies. Basically similar to above, but shows a narrow 350 km/s peak near 2 kpc.