Comparison of the ionizing photon rates computed from Hα emission line and from the fit obtained with the analysis of the stellar populations with BaySeAGal (left; see text in Sect. 6.3). The dashed black line represents the 1:1 relation. μ and σ are the bias and the standard deviation. Right panel: difference between these quantities as a function of the EW of Hα. Density contours are drawn in black. In both cases, the galaxies are color-coded with the extinction of the interstellar gas calculated from the Balmer decrement.