Surface density profiles of planetesimals with Discs A (upper panel) and B (lower panel). The light blue and orange plots represent the planetesimal surface density with the normal and half(noted as “slow migration”) speed of migration, respectively, with the pebble flux of Ṁ_peb = 10⁻⁴ M_E yr⁻¹ (typical case). The purple and green and the yellow and blue curves are those with Ṁ_peb = 10⁻⁵ (low pebble flux) and 10⁻³ M_E yr⁻¹ (high). The dotted lines represent the estimated equivalents (Eq. (21)). In Disc A with the high pebble flux and the half migration speed (blue), the calculation is stopped when the planet reaches about 0.9 au to save computer time. In Disc B, no planetesimals form with the low pebble flux cases.