Mean interstellar radiation field ⟨U⟩ as a function of redshift, as predicted by SIDES, illustrating the bias toward colder SEDs introduced by mm flux selections. The mean radiation field is used in SIDES to parametrize the SEDs, and a higher ⟨U⟩ corresponds to a higher dust temperature. On the right y-axis, we also indicates the corresponding peak wavelength in S_ν units of the main-sequence SED templates. The solid lines are the mean evolutions as a function of redshift for the full star-forming sample (gray), and selections at 1.2 mm (blue) and 2 mm (red), while the shaded areas and the dashed lines correspond to the 16–84% interval.