Notes. Intrinsic L_ν(1400)/L_ν(900) ratios obtained from different stellar population models: the BC03, assuming different initial mass functions (Salpeter, Salp, and Chabrier, Chab), star-formation histories (constant, cSFR, exponentially declining with τ = 0.1Gyr, exponentially rising with τ = −0.1Gyr), metallicties (Z_⊙ and 0.02 × Z_⊙), and stellar-population ages; the BPASS (Binary Population and Spectral Synthesis code Stanway et al. 2016); the Starburst99 models. We consider a range of wavelengths around 900 Å and 1400 Å, comparable to that covered by the narrow-band and the HST/ACS F606W filters in the rest frame, to estimate the average L_ν. As described in Bruzual & Charlot (2003), BC03 provides the spectral energy distribution of stars obtained from a comprehensive library of theoretical model atmospheres (KBFA in the table). The library consists of Kurucz (1996) spectra for O-K stars, Bessell et al. (1991) and Fluks et al. (1994) spectra for M giants, and Allard & Hauschildt (1995) spectra for M dwarfs. In BPASS the stellar evolutionary tracks contain a contribution from isolated stars and binary systems. Also, the stellar atmosphere models are selected from the BaSeL v3.1 library (Westera et al. 2002), supplemented by Wolf-Rayet stellar atmosphere models from the Potsdam PoWR group (Hamann & Gräfener 2003). With Starburst99, it is possible to generate SEDs assuming a bunch of stellar evolutionary tracks, including stars with and without rotation (GenevaV40 and GenevaV00 respectively, Leitherer et al. 2014), and stellar atmospheres (the combination of model atmosphere from Pauldrach et al. 1998; Hillier & Miller 1998, is the recommended option). The 70%ROT+30%noROT entry indicates a model that is a combination of GenevaV40 for the 70% and GenevaV00 for the 30% (Levesque et al. 2012). The GenevaV40 and GenevaV00 tracks were released for metallicity equal to Z = 0.014 (~Z_⊙, Eldridge 2012). The change in the intrinsic ratio due to the different evolutionary tracks and stellar atmospheres is shown for a Salpeter IMF, Z_⊙, cSFR, and 100 Myr old stellar population. In the bottom part of the table, we report the ratios calculated from the best fit templates of AGN (Bongiorno et al. 2012), in which the SEDs are dominated by the radiation coming from an (un-)obscured AGN. ⁽¹⁾ The intrinsic L_ν(1400)/L_ν(900) ratio for an unobscured TypeII AGN can be as low as 2.35 (Richards et al. 2006). In the estimation of the ratios we take into account the HI absorption occurred in star atmospheres, but we neglect that within the interstellar and circum-galactic medium.