NGC 4254: A Spiral Galaxy with an M = 1 Mode and Infalling Gas

We present high-resolution H I and Hα observations of the spiral galaxy NGC 4254. The observations were obtained with the VLA and the Maryland-Caltech Fabry-Perot camera, respectively. NGC 4254 is unusual in having a grand-design spiral structure with a strong m=1 component for which there is no obvious cause in optical images. Our observations reveal that, in addition to the usual galactic disk component, there are H I clouds superposed on and beyond the H I disk, at velocities up to 150 km s −1 from those established for the disk. The mass in these clouds is ∼2.3×10 8 M ○. , and they may be the remnants of an entity that was tidally disrupted by NGC 4254 and is now merging with it