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

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90 3 • IFS of a GEHR in NGC 6946 PPak-field Knot A Knot B Knot C Knot D n([Sii]) 55: 61 ± 20 98: 77: 73: a t([Oiii]) b 0.78 ± 0.06 0.87 ± 0.06 0.80 ± 0.13 0.78 ± 0.10 · · · t([Oii]) 0.83 ± 0.11 0.80 ± 0.07 0.87 ± 0.13 c 0.78 ± 0.15 · · · t([Siii]) 0.61 ± 0.13 d 0.71 ± 0.12 0.63 ± 0.20 d 0.61 ± 0.17 d · · · a Assuming a mean temperature from the temperature measured in the other knots b [Oiii] temperatures measured in the mosaic c From a relation with T([Oiii]) based on photoionization models d From an empirical relation with T([Oiii]) Table 3.7: Electron densities and temperatures for the integrated spectra of the PPak-field and the four knots. Densities in cm −3 and temperatures in 10 4 K. when required, the unseen ionization stages of each element, resorting to the most widely accepted ICFs for each species: X H = ICF (Xi ) X+i H + Helium abundance We have measured emission fluxes for 3 lines of Hei and one of Heii. The spectra presented other helium lines, although all of them were blended with another emission line or were so weak that they cannot be used to derive the helium abundance with the necessary accuracy. We have therefore used the Hei λλ 4471 (only found in knot A), 5876, 6678 and 7065, and Heii λ 4686 lines to estimate the abundances of helium once and twice ionized, respectively. Helium lines arise mainly from pure recombination; however, they could have some contribution from collisional excitation as well as be affected by self-absorption and, if present, by underlying stellar absorption (see Olive and Skillman, 2001, for a complete treatment). We have taken the electron temperature of [Oiii] as representative of the zone where the He emission arises and we have used the equations given by Olive and Skillman (2001) to derive the He + /H + value (see Appendix B). We have not taken into account, however, the underlying stellar population and the corrections for fluorescence, since the involved helium lines have a negligible dependence with optical depth effects and the observed objects have low densities. As we have seen in section 3.4.7, the integrated spectra of the PPak-field and three of the four knots show in their spectra the signature of the presence of WR stars by the blue bump around λ 4600. For this reason, we have taken care when measuring the emission-line flux of Heii λ 4686. To calculate the abundance of twice ionized helium, we have resorted to the work by Kunth and Sargent (1983). Then, for the total abundance, we have directly added the two ionic abundances:
3.4. Results 91 PPak-field Knot A Knot B Knot C He + /H + (λ4471) · · · 0.079 ± 0.010 · · · · · · He + /H + (λ5876) 0.082 ± 0.007 0.083 ± 0.004 0.075 ± 0.010 0.094 ± 0.009 He + /H + (λ6678) 0.074 ± 0.011 0.078 ± 0.005 0.070 ± 0.018 0.060 ± 0.007 He + /H + (λ7065) 0.084 ± 0.018 0.079 ± 0.007 0.110 ± 0.038 0.074 ± 0.016 He + /H + (Adopted) 0.080 ± 0.007 0.080 ± 0.004 0.076 ± 0.035 0.073 ± 0.025 He 2+ /H + (λ4686) 0.0008 ± 0.0003 0.0005 ± 0.0002 · · · 0.0003 ± 0.0001 (He/H) 0.080 ± 0.007 0.081 ± 0.004 · · · 0.073 ± 0.025 Table 3.8: Ionic and total chemical abundances for helium. He H = He+ + He 2+ H + The results obtained for each line and their corresponding errors are presented in Table 3.8, along with the adopted value for He + /H + (a weighted average of the values deduced from each of the lines). Ionic and total chemical abundances from forbidden lines The oxygen ionic abundance ratios, O + /H + and O 2+ /H + , were derived from the [Oii] λλ 3727,3729 Å and [Oiii] λλ 4959, 5007 Å lines, respectively using the appropriate electron temperature for each ion. The total abundance of oxygen was derived assuming O H ≈ O+ + O 2+ H + Regarding the sulphur, we derived S + abundances from the fluxes of the [Sii] emission lines at λλ 6717, 6731 Å assuming that T([Sii]) ≈ T([Oii]); S 2+ abundances have been derived from the fluxes of the near-IR [Siii] λ 9069 line and the directly measured T([Siii]) for knot A and its estimated value for the other knots. The total sulphur abundance was calculated using an ionization correction factor (ICF) for S + +S 2+ according to Barker (1980) formula, which is based on the photoionization models of Stasińska (1978): ICF (S + + S 2+ ) ≈ [ ( ) O 2+ α ] −1/α 1 − O + + O 2+ where α = 2.5 provides the best fit to the scarce observational data on S 3+ abundances (Pérez-Montero et al., 2006). Taking this ICF as a function of the ratio O 2+ /O instead of O + /O reduces the propagated error for this quantity. The ionic abundance of nitrogen, N + /H + , was derived from the intensities of the λλ 6548,
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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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140 4 • Long-slit spectrophotomet
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150 Conclusions and future work has
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152 Conclusions and future work oth
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154 Conclusions and future work The
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156 Conclusiones Las abundancias to
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158 Conclusiones consistentes con l
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160 Appendix A where c=0.434C. This
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162 Appendix B where R S2 = I(6717
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164 Appendix B Sulphur As in the ca
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166 Appendix B Argon For argon, the
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Appendix C Empirical calibrators In
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C • Empirical calibrators 171 One
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Appendix D Stellar photometry resul
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D • Stellar photometry results of
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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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