NED object is MESSIER 081; Reference is 1975ApJ...195...23G

   FIG. 3.-The projected column density of the neutral hydrogen on the sky. The
 contour units are in percent of the peak value, which is 2.7 x 10**(21)
 cm**(-2) projected on the sky. The optical center of M81 is indicated with a
 +. The positions at which the non-circular motions caused by a density wave
 perturbation were calculated (see {section} VII) are indicated with a {solid
 dot}.