Migration maps for disk1 model panel a and disk2 model panel b. The color indicates the migration timescale which is calculated using Paardekooper et al. (2011). In the blue region, particles migrate inward, while they undergo outward migration in the red region. Snapshots of simulations are overplotted by filled circles (Σ₀ = 15), open squares (Σ₀ = 30), and filled triangles (Σ₀ = 75). When the disk has a flat slope (panel a), the type I migration can be significantly suppressed.