Left four panels: frequency histograms of a_IR for different hybrid tracers as a function of stellar mass. Massive galaxies (log[M_∗/M_⊙] > 10.5) appear in red, intermediate-mass galaxies (10 < log  [M_∗/M_⊙] < 10.5) are shown in gray, and low-mass galaxies (log[M_∗/M_⊙] < 10) in blue. Dashed vertical lines correspond to the median value of each galaxy group. Black top marks show the median value for all the galaxies as in Fig. 16. There is a clear trend with the stellar mass that less massive galaxies need a higher value of the a_IR coefficient compared with massive galaxies. Right four panels: same as in left panels, except this time type-2 AGNs are excluded for the sample. The distribution of the a_IR coefficient with the stellar mass and morphological type (Fig. 17) allow us to provide, for the first time, a set of hybrid calibrations in terms of these galaxy properties. If the sample to be analyzed is biased toward morphology or, more commonly, luminosity or stellar mass, these tracers would be particularly useful (see Tables 4 and 5).