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

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132 4 • Long-slit spectrophotometry of multiple knots of Hii galaxies 2.4 2.2 2.0 1.8 HII galaxies Hagele et al. (2006,2008) Knots J1657 N e = 10 cm -3 N e = 100 cm -3 t e ([OII]) 1.6 1.4 1.2 1.0 IZw18 SE IZw18 NW N e = 500 cm -3 0.8 0.6 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 t e ([OIII]) Figure 4.12: Relation between t e ([Oii]) and t e ([Oiii]), for the knots of J1657, the objects studied by Hägele et al. (2006) and Hägele et al. (2008), and Hii galaxies from the literature. The red dashed lines correspond to photo-ionization models from Pérez-Montero and Díaz (2003) for electron densities N e = 10, 100 and 500 cm −3 . The model sequences from (Stasińska, 1990, solid line) are also shown. Temperatures are in units of 10 4 K. criteria for J1657 (see Hägele et al., 2008) was high Hβ flux and large equivalent width of Hα, which tends to select objects with abundances and electron temperatures close to the median values shown by Hii galaxies. To our knowledge, there is no previous reported t e ([Oiii]) for this galaxy in the literature. Figure 4.12 shows the relation between the [Oii] and [Oiii] temperatures measured in the three knots of J1657. Also shown in the Figure are the corresponding values for Hii galaxies as derived from the emission line intensities compiled from the literature and the objects studied by Hägele et al. (2006) and Hägele et al. (2008). In Table 13 of Hägele et al. (2008) are listed the values together with the references that have been used. This compilation is restricted to objects for which the temperatures could be derived with an accuracy better than 10%. An exception has been made for IZw18. In this case, the large errors in the derived [Oii] temperatures (30% and 40% for T e ([Oii]) in the NW and SE knots respectively), are probably related to the low oxygen abundance in this galaxy and hence the weakness of the involved emission lines. These points are labelled in the Figure and, due to their large values, no error bars in t e ([Oii]) are shown. The relation between the [Oii] and [Oiii] temperatures does not show a clear trend, show-
4.4. Discussion 133 2.2 2.0 HII Galaxies Hagele et al. (2006,2008) J1657 Knots 1.8 t e ([SII]) 1.6 1.4 1.2 1.0 n e = 10 cm -3 n e = 100 cm -3 0.8 0.6 0.4 0.8 1.0 1.2 1.4 1.6 1.8 t e ([OII]) Figure 4.13: Relation between t e ([Sii]) and t e ([Oii]) for knots of J1657, the objects studied by Hägele et al. (2006) and Hägele et al. (2008) and Hii regions from the literature. The solid line represents the one to one relation. The red dashed lines correspond to the photo-ionization models from Pérez- Montero and Díaz (2003) for electron densities N e = 10 and 100 cm −3 . Temperatures are in units of 10 4 K. ing a scatter which is larger than observational errors. As it was mentioned in Chapter §3, the [Oii] temperature is somewhat dependent on density. The density effect can be seen by looking at the model sequences which are overplotted and which correspond to photo-ionization models from Pérez-Montero and Díaz (2003) for electron densities N e = 10, 100 and 500 cm −3 . This relationship was used to derived the [Oii] temperature for Knot B in NGC 6946 and for IIZw71. Higher density models show lower values of t e ([Oii]) for a given t e ([Oiii]). The effect is more noticeable at high electron temperatures. The data points populate the region of the diagram spanned by model sequences with most objects located between the model sequences corresponding to N e 100 and 500 cm −3 . The three knots of J1657, however, lie between the model sequences for N e 10 and 100 cm −3 (in fact, very close to the first one), which is consistent with the derived values of the density. The standard procedure in principle adopted for the analysis of low resolution and poor signal-to-noise data is to use the (not unique) relation between the [Oii] and [Oiii] temperatures which is now extended to data of much higher quality. The solid line in Figure 4.12 shows the relation based on the photo-ionization models by Stasińska (1990), adopted in
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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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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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