A snapshot of run 3D.Z2 taken at t = 150 orbits (Z = 0.02). Image a) is the view from the side (x − z plane). Image b) is the view from above (x − y plane). The color scale marks the column solid density normalized to the initial gas density (Σ_solid/ Σ_gas,0). The two images have a different color scale, since the column density in the azimuthal direction is much higher. Note that the particle structure is nearly axisymmetric.