Torque map for a pebble disk characterized by the radial mass flux Ṁ_p = 10⁻⁴ M_⊕ yr⁻¹. For each Stokes number, St, we obtain Σ_p from Ṁ_p (Eq. (A.1)), which results in the pebble-to-gas mass ratio, Z, decreasing with increasing St, as shown in the upper horizontal axis. The value of Z is used to rescale the results of Fig. 2. We show the total torque (exerted by both pebbles and gas) scaled by the gas-driven torque for simulation sets MspE1 (top) and MspE0 (bottom). In the top panel, the total torque is always negative and planet migration is directed inwards. In the bottom panel, a subset of the parameter space exists for which the total torque is positive, resulting in outward migration.