Dimensionless surface density of spiral arms (m = 1) for Model A. The six panels in the upper left corner are the spiral arms for more massive disks (M_disk/M_• = 0.8), and the six panels in the lower right corner are those for less massive disks (M_disk/M_• = 0.2). The values of , M_disk/M_•, and R_out/R_in are marked on the top of each panel. In general, more massive disks have more loosely wound spiral arms (see more details in Sect. 3.2). The eigenvalues (real and imaginary parts) of ω are also provided in each of the panels.