Thermal relaxation times normalized by the critical cooling time t_crit (top) and the orbital frequency (bottom) at r = 5.5 au for f_dg = 10⁻³, assuming only radiative cooling (t_rel = t_cool), including the effect of dust collisions (), and including gas emission with defined in Eq. (13). Also shown are the corresponding values for t_rel = t_crit. The gas opacities reported in Freedman et al. (2008), Malygin et al. (2014, 2017) for solar abundances correspond to .