The approach we have followed in order to derive a robust estimation for the maximum oxygen abundance in spiral galaxies is to use new abundance-derivation tools. This approach is based on firm physical assumptions that are independent of the particular temperature structure in H ii regions, as shown inFigure 18.1 (Pilyugin et al. 2006). In order to derive O/H abundances consistently for our extended sample of H ii regions in galaxies, the ff relation (Pilyugin 2005) between nebular and auroral [O iii] line fluxes has been used. The relation between T[O iii] and T[OII] temperatures presented in Figure 18.1 (left) was derived by Pilyugin et al. (2006) by applying nebular boundary conditions to the H Ii-region ionization structure, giving t2 = 0.72t3 + 0.26, where t2 = T[OII]/104 and t3 = T[OIII]/104. In Figure 18.1 (right), the ff relation shows a tight correlation between [O iii] A4363/H| (R) and [O iii] H4959, 5007/H| (R3), which appears to hold for high-abundance (log(O/H) > -3.75) H ii regions (Pilyugin 2005; Pilyugin etal. 2006). The expected value of the electron temperature of an H ii region can be derived using this ff relation.
this study *
Oey and Shields (2000)
Figure 18.1. Left: a model-independent relation between the expected electron temperatures corresponding to [O iii], t3, and , t2 (in units of 104 K), compared with other derivations in the literature (Pilyugin et al. 2006). Right: the ff relation of Pilyugin (2005) between the flux ratios of auroral, [O iii] X4363/HP (R), and nebular, [O iii] XX 4959, 5007/HP (R3), lines of [O iii]; see the text for details.
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