Gas and dust temperature (first row), derived H₂ volumetric density from the HNC J=4–3/J=1–0 ratio (second row), and derived N₂H⁺ J=1–0 and HCO⁺ J=1–0 column density (third row) vs. source bolometric luminosity L_bol (left column) and envelope mass M_env (right column). In the bottom row, the error bars are about the size of the plotted points. The starless cores (squares) HH211, and L1445 IRS2 adopt the average H₂ volume density for their respective region (see Table A.5).