Gas, pebble, and planetesimal surface density. The purple, green, and light blue solid plots represent these profiles, respectively, with Discs A (upper panel) and B (lower panel) at t = 3.8 × 10⁵ yr. The pebble flux is Ṁ_peb = 10⁻⁴ M_E yr⁻¹ and the migration speed is the normal one. The purple, green, and light blue dotted lines represent the unperturbed gas surface density (Eq. (19)), the unperturbed pebble surface density (Eq. (10), and the estimated planetesimal surface density (Eq. (21)), respectively.