The dependence of the effective diffusion on the number density of active bath particle ρ. Dots and corresponding error bars are simulation results of D_eff. Solid lines are the numerical calculations of D_eff. Both results show that, with the increase of activity D_b, effective diffusion D_eff gradually changes from monotonic decrease to monotonic increase with the number density of bath particle ρ, including a non-monotonic interval around D_b=2.0. Herein, τ_b is set as 0.1.