Relation between local extragalactic gas density and star formation activity of star-forming galaxies in SIMBA at z = 0 (blue), 1 (green), and 2 (red). Top row: sSFR as a function of the local external gas density. Bottom row: Stellar mass-corrected sSFR offset from the main sequence as a function of the local external gas density. The panels show the 2D scatter, with 1, 2, and 3σ density contours in black. We also show the best-fit power-law relation for galaxies with ρ_ext > 10⁻ M_⊙ ckpc⁻³), with shaded areas indicating the 1σ uncertainty.