Top panels: comparison between the EW of Hδ, Hβ and Paβ lines to the dust attenuation parameter A_Paβ, IRX, defined as 2.5 × log₁₀(1 + SFR_IR/SFR_Paβ, obs) (Paper I). We remark that the last panel is equivalent to the bottom-right plot in Fig. 3, even though a different scale has been used (the relation between A_Paβ, IRX and A_V, tot is given in Eq. (1)). Bottom panels: correlations between the EW of Hδ, Hβ, Paβ lines and the N2 index (=log₁₀([NII]/Hα)). The blue continuous lines are the best-fit linear relations, determined as explained in Sect. 3, while the blue shaded area show the ±1σ scatter of our data around the best-fit relations.