Maps of the low-energy spectral slope (α, upper row) and of the CR ionisation rate (ζ_ion, lower row) as a function of the energy surface brightness expected by direct CR excitation for the four H₂ rovibrational transitions listed in Table 1 and as a function of the H₂ column density. We note that we assume . The dashed black lines show the expected brightness due to indirect excitation by interstellar UV photons for a far-UV radiation field with G₀ = 1.7 (Draine 2011). Solid black lines show the iso-contours of α (upper panels) and ζ_ion in units of 10⁻¹⁷ s⁻¹ (lower panels). Solid blue horizontal lines show the JWST sensitivity for a signal-to-noise ratio of 3 over 1.25 h of integration, adding up the signal over 50 shutters. Solid green horizontal lines show the X-shooter sensitivity for a signal-to-noise ratio of 3 over 8 h of integration, adding up the signal over the whole slit.