A spatially resolved study of ionized regions in galaxies at different ...

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138 4 • Long-slit spectrophotometry of multiple knots of Hii galaxies 0.0 -0.2 HII Galaxies WHT objects J1657 Knots IIZw71 Knots -0.4 log (Ne/O) -0.6 -0.8 -1.0 -1.2 -1.4 7.0 7.5 8.0 8.5 12+log(O/H) -1.2 -1.4 HII Galaxies Hagele et al. (2006,2008) J1657 Knots IIZw71 Knots -1.6 -1.8 log (Ar/O) -2.0 -2.2 -2.4 -2.6 -2.8 -3.0 7.0 7.5 8.0 8.5 12+log(O/H) Figure 4.16: Ne/O (upper panel) and Ar/O (lower panel) ratios as a function of 12+log(O/H) for the knots of J1657 (filled yellow diamonds), knots of IIZw71 (filled red triangles), the objects of Hägele et al. (2006) and Hägele et al. (2008) (blue circles) and the Hii galaxies (open squares) from the literature. The solar values are shown with the sun symbol; oxygen from Allende Prieto et al. (2001) and from Grevesse and Sauval (1998) for neon and argon. These values are linked by a solid line with the solar ratios from Asplund et al. (2005).
4.4. Discussion 139 to giant Hii regions. As we have seen from previous sections, the derived ionic abundances knots B and C are very similar. However, due to the lack of auroral lines in the spectra of knots A and D, no temperatures have been derived and therefore, no ionic abundances. The calculation of metallicities in these two knots can only be carried out with calibrations based on the strongest emission lines, as we did in Chapter §3 for knot D of NGC 6946. The different strong-line methods for abundance derivations, which have been widely studied in the literature, are based on directly calibrating the relative intensity of some bright emission lines against the abundance of some relevant ions present in the nebula (see Appendix C for details on the definition and equations of the parameters used in this work). For the case of oxygen, we take the calibrations studied by Pérez-Montero and Díaz (2005), who obtain different uncertainties for each parameter in a sample of ionized gaseous nebulae with accurate determinations of chemical abundances in the whole range of metallicity. In Figure 4.17, we show the corresponding total abundances as derived from several strong-line methods and the oxygen abundances calculated from the electron temperatures measured in knots B and C. Among the available strong-line parameters we studied the O 23 parameter (also known as R 23 and originally defined by Pagel et al. (1979) and based on [Oii] and [Oiii] strong emission lines). This parameter is characterised by its double-valued relation with metallicity, with a very large dispersion in the turnover region. According to the values measured in knots B and C, we used the McGaugh (1991) calibration for the lower branch, obtaining similar values for the oxygen abundance in the four observed knots. The N2 parameter (defined by Storchi-Bergmann et al., 1994) is based on the strong emission lines of [Nii]. It remains single-valued up to high metallicities in its relation to oxygen abundance, and it is almost independent of reddening and flux calibrations. Nevertheless, it has the high dispersion associated to the functional parameters of the nebula (ionization parameter and ionizing radiation temperature) and to N/O variations. We used the empirical calibration of this parameter from Denicoló et al. (2002) to derive the oxygen abundance in the four knots of this galaxy. We can see in Figure 4.17 that the abundances predicted by this parameter are quite similar for all the knots although higher than the values derived from the direct method in knots B and C. The S 23 parameter was defined by Vilchez and Esteban (1996) and is based on the strong emission lines of [Sii] and [Siii]. The calibration done by Pérez-Montero and Díaz (2005) yields oxygen abundances comparable for the four observed knots, slightly higher than the directly derived abundances of knots B and C, but still consistent with them within the errors. In the case of sulphur, both the directly and empirically derived abundances of knots B and C are slightly different with knot C showing a lower abundance. However it should be remembered that the near IR sulphur lines relative to the hydrogen recombination lines are more affected by reddening than in the case of oxygen when no Paschen lines are observed, which is the case.
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Facultad de Ciencias Departamento d
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A Abigaíl, mi ut A mi familia, por
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La gente del grupo de Astrofísica
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Contents List of Figures List of Ta
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CONTENTS iii B •Physical conditio
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vi LIST OF FIGURES 3.12 Example of
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List of Tables 1.1 Integrated prope
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Chapter 1 Introduction 1.1 Overview
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1.1. Overview 3 Figure 1.1: Sample
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1.1. Overview 5 These massive star
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1.1. Overview 7 Figure 1.3: Color-m
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1.2. Aims and structure of this wor
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12 2 • The star formation history
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40 3 • IFS of a GEHR in NGC 6946
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β[H 84 3 • IFS of a GEHR in NGC
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190 REFERENCES Bertelli, G., Bressa
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192 REFERENCES Girardi, L. & Bertel
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194 REFERENCES Kunth, D. & Sargent,
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196 REFERENCES Pérez-Montero, E.,
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198 REFERENCES Terlevich, R., Melni
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