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

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78 3 • IFS of a GEHR in NGC 6946 1e−15 2.5 WR blue bump Flux (erg cm−2 s−1 ◦A−1 ) 2.0 WR red bump 1.5 4600 4800 5000 5200 5400 5600 5800 Wavelength (◦A) Figure 3.21: Detail of the integrated spectrum of knot A with the identification of both the blue (4650Å) and red (5808Å) Wolf-Rayet bumps over the adopted continuum, marked as a dashed (green) line. 3.4.7 Wolf-Rayet stellar population Wolf-Rayet (WR) stars appear in the first stages after the main sequence of massive stars, so they are already visible early after the beginning of the burst of star formation (approximately 2 Myr). The WR phase lasts on average until ∼ 5 Myr. The strength of the stellar winds produced by these stars is sometimes measured in the integrated spectra of the starburst galaxies, which are identified as WR galaxies (Conti, 1991). The presence of the bumps produced by WR stars are therefore associated with the existence of processes of intense star formation. The existence of this WR stellar population can be very useful for the study and characterization of the ionizing stellar population in starburst galaxies (e.g. Pérez-Montero and Díaz, 2007). These WR features are the blue bump, centred at 4650 Å and produced mainly by broad emission lines of Nv at 4605, 4620 Å, Niii 4634, 4640 Å, Ciii/iv 4650, 4658 Å and Heii at 4686 Å. The red bump, usually fainter, is centred at 5808 Å and is emitted mainly by Ciii/iv. In addition to the initial mass of the star, another fundamental parameter in WR stars is metallicity. Increasing the content of heavy elements, increases the ratio of mass loss due to winds. Thus, the more metal rich is the star, the lower will be the initial mass needed
3.4. Results 79 to become a WR star. To estimate the number of WR stars in a resolved cluster it is only necessary to count them. For an unresolved cluster, the equivalent width of the blue bump (WR λ 4650) or the ratio between this bump and the Hβ emission line are used as diagnostics. The values of these quantities in the range of interest (2-6 Myr) depends strongly on metallicity. We have detected the blue bump in several fibers on the IFU data, while the red bump was only marginally detected when summing the emission of the whole knot A. In Figure 3.21 we show the broad emission of both the blue and red bumps (the last one very weakly detected) for the integrated flux for knot A. The blue bump is remarkably strong in the integrated spectrum of this knot. In section 3.4.8 the integrated properties of the knots are described. Figure 3.22 shows the WR spatial distribution in the PPak field. The filled dark (violet) regions represent the fiber detections of the blue WR bump. On the upper panel the Hα contours are overplotted, while in the lower panel the continuum contours near the WR emission (∼ λ 4500 Å) are shown. The filled regions only represent positions of the WR stars in the field, not intensity. Clear detections where found in 10 fibers of knot A, corresponding to the extended region in that location. On the other hand, only in one fiber of knot B was found a weak blue bump, while in knot C two fibers showed a medium-intensity feature. As it is clearly seen, the location of the bumps follow very well the morphology of the continuum emission adjacent to the WR blue bump. We also verified that the maximum of the continuum emission adjacent to Hβ corresponds spatially to the WR bumps intensity maximum. Interestingly, knot B shows a weak WR blue bump. Although the continuum there has very low surface brightness, the local peak intensity matches as well the position or the detected feature. As we see from top panel of Figure 3.22, the location of the WR blue bump coincides with the morphology of the Hα emission, although there are slight offsets from their peak intensity, particularly in knots B and C. The bumps have been measured in the following way. First a continuum shape has been adopted and we have measured the broad emission over this continuum in the wavelengths of the blue bump, at 4650 Å. Finally, we have subtracted the emission of the narrower lines not emitted by the WR winds, which are [Feiii] 4658 Å, Heii 4686 Å, Hei + [Ariv] 4711 Å and [Ariv] 4740 Å in the blue bump (although these last two lines present very small contribution). The dereddened relative intensities and the equivalent widths of the blue bump are shown in Table 3.3. Although some contribution of the red bump was found in knots A and C, the flux could not be measured with an acceptable accuracy. No detection of blue or red bump was found in knot D. All measurements were performed in the integrated spectra from the mosaic, so that the reported values have been derived from absolute fluxes.
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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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Page 48 and 49: 28 2 • The star formation history
Page 60 and 61: 40 3 • IFS of a GEHR in NGC 6946
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128 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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