Midplane pebble-to-gas ratio Z = ρ_p /ρ_g in the α_mid/α_acc − F_p/g space (Eq. (10)). Top and bottom panels correspond to α_acc = 10⁻² and α_acc = 10⁻³, respectively. Left and right panels correspond to τ_s = 0.01 and τ_s = 0.1, respectively. The color contours are obtained by directly solving Eq. (10). The red-colored regions indicate the “no-drift” runaway pile-up (i.e., ρ_p/ρ_g goes to infinity; no-solution). The calculations correspond to r = 5 au, but the results depend very weakly on the radial distance to the star. The ND mode can occur irrespectively of the radial shape and position of a dead zone (see more details in Paper I). We note that the physics of planetesimal formation is not included here.