Synthetic emission spectra of GJ 3470b corresponds to the grid of 16 models and the standard model. Each colour corresponds to a set of metallicity and thermal profile. A colour gradient is then used to differentiate the eddy diffusion coefficients and stellar UV fluxes (see legend in the top panel and meaning of each symbol in Table 2). The standard values are shown in Figs. 2 and 3. The standard metallicity is 10× solar (ζ = 10).