Space-time plot of runs with τ_s = 10⁻³, 10⁻², 10⁻¹, 10⁰ and 10¹ with respect to radial coordinate, x and orbital time. The y-axis on the right-hand side shows the metallicity, Z. The colors correspond to the solid surface density and the orange line to ρ_p,max ∕ρ_g = 100. This criteria fits well with the start of filament formation in all systems, except in the first panel, where τ_s = 10⁻³. Here, the limit is reached without the formation of any visible filaments.