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Appendix A: Distribution of H II regions across other diagnostic diagrams

This study has been focused on study how the imprint of the chemical evolution in galaxies has affected the distribution of H ii regions across the most widely used diagnostic diagram, the so-called BPT diagram (e.g., Fig. 1). In this Appendix we show that this imprint not only affects the location within the BPT diagram. Indeed, in basically all the explored diagnostic diagrams, we find clear trends related to the properties of the underlying stellar population. Figure A.1 shows four additional diagnostic diagrams, different than the BPT diagram, built based on the comparison of the following emission line ratios: [O iii] λ5007/Hβ, [N ii] λ6583/Hβ, [O ii] λ3727/Hβ, [S ii] λλ6717, 31/Hβ, and [O iii] λ5007/[O ii] λ3727. Each of these line ratios is more sensitive to different properties of the ionized gas and the ionizing sources. It is beyond the scope of this study to describe the particular dependencies of each one in detail, but they have been widely described in the literature

Fig. A.1 Distribution of the ~5000 H ii regions included in our sample across four classical diagnostic diagrams: top left panel, [O iii] λ5007/Hβ vs. [O ii] λ3727/Hβ; top right panel, [O iii] λ5007/Hβ vs. [S ii] λ6717, 31/Hβ; bottom left panel, [O iii] λ5007/[O ii] λ3727 vs. [N ii] λ6583/Hβ and bottom right panel, [O iii] λ5007/[O ii] λ3727 vs. [S ii] λ6717, 31/Hβ. In each panel, the contours show the density distribution of the H ii regions within considered diagram, with the outermost contour enclosing 95% of the regions, and each consecutive one enclosing 20% less regions. The color indicates the average luminosity weighted age of the underlying stellar population at the corresponding location in the diagram. The solid line represent the classical demarcation line used to select H ii regions.

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(e.g., Veilleux & Osterbrock 1987; Dopita & Sutherland 1995; Cid Fernandes et al. 2010). However, regardless to which physical properties are more sensitive, Fig. A.1 shows that it is possible to identify trends in the luminosity-weighted age of the underlying stellar population in the four diagrams. In some cases the trend is stronger for one of the explored line ratios; e.g., in the [O iii] λ5007/Hβ vs. [S ii] λλ6717, 31/Hβ diagram, the stellar age is more clearly associated with the first of the two parameters, while in the [O iii] λ5007/[O ii] λ3727 vs. [N ii] λ6583/Hβ diagram, it is more clearly related to the second one. However, even in the case of the diagnostic diagram comparing the two line ratios with the apparent weaker dependence with the age of the stellar population ([O iii] λ5007/[O ii] λ3727 vs. [S ii] λ6717, 31/Hβ), there are clear trends that depend on the two parameters at the same time.

In summary, we have shown that the main conclusion of the current study, i.e., that there is a tight relation between the properties of the H ii regions and those of the underlying stellar population, is independent of the diagnostic diagram selected to explore this depedence.

© ESO, 2015