IR luminosity surface density, Σ_IR, as a function of starburstiness, R_SB. Blue and orange filled dots separate galaxies on and three times above the MS. The letters indicate the morphology. The median position of mergers (M) and “single/isolated” (S) galaxies are indicated at the bottom with a red triangle and a blue triangle, respectively. The blue star shows the position of typical z ~ 2 MS galaxies.The most massive galaxies (M_⋆ > 10¹¹ M_⊙) are surrounded with an open circle.