Neutral hydrogen observations of the edge-on disk galaxy NGC 891.

Results are presented for 21-cm hydrogen line observations of the edge-on spiral galaxy NGC 891 with the Westerbork Synthesis Radio Telescope. It is found that: (1) the H I disk ends with the bright optical disk on one side (at about 6 arcmin) and extends out to 9 arcmin on the other; (2) the rotation curve is approximately flat out to the edge of the bright optical disk, well within the Holmberg radius; (3) the angle of inclination is at least 87.5 deg; (4) there is no significant bending of the H I layer; (5) the H I is confined to the plane, with a thickness of less than 1 kpc in the inner regions, but the equivalent thickness apparently increases up to 1-2 kpc at a radius of 5-6 arcmin; and (6) there are morphological similarities between NGC 891 and the Galaxy.