The intrinsic L_Hβ/L_UV ratio for the 11 AMAZE objects (histogram) where total L_UV is estimated from best-fit SED-fitting results and L_Hβ is computed from the observed Hβ fluxes. L_UV is the intrinsic UV luminosity of the best-fit models, L_Hβ has been corrected for dust extinction as described in Sect 3.2. Red vertical lines show the L_Hβ/L_UV at increasing time from the end of 10 Myr truncated star-formation burst models. Line emission in models is estimated as described in Sect. 3.