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

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94 3 • IFS of a GEHR in NGC 6946 Radius F(Hα) L(Hα) Q(H 0 ) M(Hii) (pc) (erg cm −2 s −1 ) (erg s −1 ) (photon s −1 ) (M ⊙ Knot A 190 1.93 × 10 −12 8.03 × 10 39 7.9 × 10 51 2.5 × 10 5 Knot B 95 1.08 × 10 −13 4.52 × 10 38 4.5 × 10 50 1.5 × 10 4 Knot C 115 3.76 × 10 −13 1.55 × 10 39 1.5 × 10 51 5.0 × 10 4 Knot D 100 1.51 × 10 −13 6.28 × 10 38 6.2 × 10 50 2.0 × 10 4 Table 3.10: Hα flux and derived parameters for the (mosaic) integrated spectra of the four knots. M HII = Q(H 0 ) m p n e α B The values are also listed in Table 3.10. All of them, given the assumptions of no dust absoption or photon leakage, represent lower limits. Table 3.10 also gives the estimated radius, in parsecs, of a circular aperture covering the spatial distribution of the fibers used in the integrated spectra of each knot. This value is not intended to be accurate, but to give an order of magnitude of the sizes involved. As it can be seen, the luminosities and masses of H + from this four knots are typical of giant Hii regions and can be compared to the case of NGC 5471. Knot A of NGC 6946 is about a factor of 2 more luminous than Knot 1 in NGC 5471, while Knot C is similar to Knot 2 and the other two knots are of the same order of magnitude as Knot 4 or 10. It should be noted that the spatial scales involved in each case are very different. While the effective radius of the knots of NGC 5471 are around 60 pc, in NGC 6946 the radii can be 2 o 3 times larger. 3.5.2 Derived properties of the WR population The detection and measurement of the WR blue bump in three of the four knots can be very useful for the study of the ionizing stellar population. In this way, it is possible to compare the observed relative intensities and equivalent widths of the WR bumps with the predictions of Starburst 99 (Leitherer et al., 1999) population synthesis models as a function of the metallicity, age and star formation law of the cluster. For this purpose, we have run a Starburst 99 model based on stellar model atmospheres from Smith et al. (2002), Geneva evolutionary tracks with high stellar mass loss (Meynet et al., 1994), a Kroupa Initial Mass Function (IMF; Kroupa, 2002) in two intervals (0.1-0.5 and 0.5-100 M ⊙ ) with different exponents (1.3 and 2.3 respectively), a metallicity of Z = 0.02, the theoretical wind model (Leitherer et al., 1992) and a supernova cut-off of 8 M ⊙ . In Figure 3.26 we show the predicted equivalent width and relative intensity to Hβ for
3.5. Discussion 95 20 15 EW(WR)(◦A) 10 5 0 0 2 4 6 8 10 100 100 F(WR)/F(Hβ) 80 60 40 20 0 0 2 4 6 8 10 Age (Myr) Figure 3.26: Relation between intensities and equivalent widths of the Wolf-Rayet blue bump as a function of the age of the cluster for a Z = 0.02 metallicity, according to Starburst 99 predictions. In both panels, (blue) solid lines represent instantaneous star formation and (green) dashed lines continuous star formation. The (light blue) horizontal band represents the error in the measurement of the appropriate quantity for knot A. the blue bump as a function of the cluster age for a metallicity Z = 0.02 (Z ⊙ ), the closest value according with the total oxygen abundances derived. The (blue) solid lines represent in both plots the evolution of an instantaneous burst, while the (green) dashed lines do for a continuous star formation history with a constant star formation rate. The (light blue) horizontal bands in both panels represents the error in the measurement of the appropriate quantity for knot A. As noted in section 3.4.7, the quantities plotted depend strongly on metallicity. The models predict brightest and most prominent features for higher metallicity, according with the stellar model atmospheres for WR stars (Crowther, 2007). At the same time, we notice that in the instantaneous star formation the WR features appear during the interval between 2 and 5 Myr and they reach higher intensities. On the other hand, for a continuous star formation history, the WR features appear at the same age and, despite of reaching lower intensities, they converge to a non-zero value at older ages. By comparing the relative intensities and equivalent widths of the three knots, shown in Table 3.3, we see that all of them are larger than the model-predicted values for a constant star formation law, but match fairly well with the values predicted for an instantaneous burst
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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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42 3 • IFS of a GEHR in NGC 6946
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144 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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