Presentation #107.01 in the session “Asynchronous Posters”.
Spiral galaxies’ disks are usually considered to be dominated by massive dark matter halos when the extended rotation curve, V, is flat. We derive disk surface density as a function of radius, for variable V, density wave arm pitch, i, and multiplicity, m. For a galaxy with a flat V, we derive a disk parameter, FD = 4 tan i / m, relative to 100% halo mass over the density wage region. The actual halo to 100% halo, FH = 1 - FD. For our example of flat curve spiral galaxies, we calculate FD which ranges from FD very much less than 1 for the almost all halo for tight-armed NGC 7217 to FD ≈ 1 for the almost all disk in loose-armed, NGC 3198. Our examples challenge the commonly accepted dominance of halos over all spiral galaxy disks.