Column density of C¹⁸O vs. the peak flux densities of protostellar (red triangles) and prestellar (black triangles) cores at (a) 70 μm and (b) 250 μm selected from Könyves et al. (2015). The number of prestellar cores in panel a is less than the total number because some have no 70 μm flux. A clear separation is found between prestellar and protostellar cores in panel a (shown with a dotted line). Panel b: increasing trend of the 250 μm flux density with the C¹⁸O column density suggesting that star formation is more advanced at higher column densities and that an increasing volume is affected by the ongoing star formation.