Dependence of the wavelength λ_ff in submm and mm ranges on the oxygen abundance 12 + log O/H, at which monochromatic dust emission is equal to monochromatic free-free emission. Red filled circles and blue filled circles are data for galaxies from the Herschel sample with L(Hβ) ≥ 10⁷ L_⊙ and L(Hβ) < 10⁷ L_⊙, respectively. The black solid line is the maximum-likelihood regression for the entire Herschel sample. I Zw 18 and SBS 0335−052E are encircled, while Haro 11 and II Zw 40 are surrounded by squares.