Left: /L₁₅ versus [Ne   iii]/[Ne   ii], as measured from the IRS spectra of the sources in our sample with EW_6.2 ≥ 0.4 μm. The orange and blue stars correspond to the average spectra of galaxies with IR8 ≤ 6.0 and 6.0 < IR8 < 9.0, respectively. Leftward arrows denote upper limits of the [Ne   iii]/[Ne   ii] ratio for sources with only a [Ne ii] detection Right: dust-mass-weighted luminosity (L_IR/M_dust) as a function of the hardness of the radiation field traced by the [Ne   iii]/[Ne   ii] line ratio.