Illustration of the spatial regions (here shown in velocity space) contributing to the emergent flux in a 20 M_⊙ type II SN model characterized by weak mixing for all non-IGE species, strong mixing for IGE species, and with a 9 M_⊙ H-rich envelope mass (model m20mix100vnimH9). Top panel: observer’s frame luminosity contribution δL_λ,R (Eq. (5); the map maximum is saturated at 20% of the true maximum to bias against the strong Hα line and better reveal the origin of the weaker emission) versus wavelength and ejecta velocity. The four contributing shells in this type II SN model are clearly seen (see vertical colored stripe at left), although the H-rich layers contribute most of the emergent flux. Bottom panel: emergent luminosity integrated over each shell, together with the total luminosity. In this model, the fraction of the total power emerging from the Si-rich, O-rich, He-rich and H-rich shells is 4, 20, 15, and 61%, respectively. This illustrates the contribution to the emergent total flux from the main ejecta shells (this may also be inferred from the width of lines but complicated when multiple regions contribute or when there is line overlap). Note that with our approach, IGEs are present in all shells and thus Fe I and Fe II flux contribution is present throughout the ejecta. One can also see that the flux from the Si-rich shell is mostly radiated by Ca I and Ca II (together with Fe I and Fe II, rather than by the dominant species Si).