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

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118 4 • Long-slit spectrophotometry of multiple knots of Hii galaxies Flux (erg cm -2 s -1 Å -1 ) 6e-16 4e-16 [OII] 3727,29 Å [NeIII] 3869 Å IIZw71 - Knot C Hδ 4102 Å Hγ 4340 Å [OIII] 4363 Å Hβ 4861 Å [OIII] 4959 Å Flux (erg cm -2 s -1 Å -1 ) 2e-16 3e-16 2e-16 1e-16 0 -1e-16 3800 4000 4200 4400 4600 4800 5000 Wavelength (Å) Figure 4.9: Results of the STARLIGHT fit to the continuum spectral energy distribution for knot C of IIZw71, the one most affected by underlying stellar population contribution. The lower panel shows the emission line spectrum once this contribution has been removed. Bad pixels and emission lines were excluded from the final fits. The percentage of the mean deviation over all fitted pixels between observed and model spectra ranges between 7.3% in knots A and D, which have the lowest signal, to 2.9 % in knot B and 1.9% in knot C. Figure 4.9 illustrates the results of the model fitting to the spectrum of knot C. The upper panel shows the observed spectrum and the model spectrum. The lower panel shows the subtraction of the fitted stellar continuum. We measured the Balmer emission line fluxes over a linear continuum derived by hand from the observed spectra. We then compared these with the same measurements over the continuum derived from the model SSPs. This allows the equivalent widths to be corrected by the presence of absorption stellar features in these lines that cause the measured EWs to be underestimated. In Table 4.2 we summarise our results for the four brightest Balmer emission lines. For each Balmer line, the first row gives the measured equivalent width of the emission line, while the third row gives the corresponding value after the removal of the underlying absorption. The second row gives the ratio between the two. Knot C is the most affected indicating a larger contribution by the underlying stellar population, although the correction for the Hβ line only amounts to 13%, reaching 24% for the Hδ line. For the rest of the knots, only B presents a significant contribution of 13 % for the Hδ line.
4.3. Results 119 Knot A B C D EW(Hα) (Å) 270±30 130±10 40±2 140±5 f c 1.00 1.00 1.05 1.00 EW(Hα) c (Å) 270±30 130±10 42±2 140±5 EW(Hβ) (Å) 34.9±4.5 30.0±1.7 10.7±1.1 32.2±4.7 f c 1.01 1.03 1.13 1.00 EW(Hβ) c (Å) 35.2±4.7 30.9±1.8 12.1±1.3 32.2±4.9 EW(Hγ) (Å) 17.2±1.7 12.8±0.9 5.0±0.9 10.8±1.7 f c 1.03 1.03 1.19 1.00 EW(Hγ) c (Å) 17.7±1.3 13.2±1.0 6.0±1.0 10.8±0.9 EW(Hδ) (Å) 8.1±0.6 6.2±0.7 1.8±1.0 8.0±0.8 f c 1.09 1.13 1.24 1.03 EW(Hδ) c (Å) 8.8±0.6 7.0±1.0 2.3±1.0 8.2±1.0 Table 4.2: Equivalent widths of the hydrogen recombination lines Hβ, Hγ and Hδ as measured directly in the spectra of the observed knots of IIZw71 once the underlying stellar populations have been removed, with the corresponding correction factors. In the case of J1657, the effect of the underlying population is not so strong. Following the procedures by Hägele et al. (2008), a pseudo-continuum has been defined at the base of the hydrogen emission lines to measure the line intensities and minimize the errors introduced by the underlying population. Hägele et al. (2008) compared the results obtained from this method with a multi-Gaussian fit to the absorption and emission components of the galaxy, finding that the difference between both methods for all Balmer lines is, within the observational errors, almost inappreciable for the stronger lines. Nevertheless, for this galaxy, the absorption wings in the Balmer lines were not prominent enough as to provide sensible results by the later method. Therefore, we have doubled the error derived using the expression for the statistical errors associated with the observed emission fluxes, (σ l ), as a conservative approach to include the uncertainties introduced by the presence of the underlying stellar population. We also applied STARLIGHT code in J1657 to separate the emission spectra from the underlying stellar absorptions, but for the strongest emission lines the differences between the measurements made after the subtraction of the STARLIGHT fit and the the ones made using the pseudo-continuum are well below the observational errors. The absorption features of the underlying stellar population may also affect the helium emission lines to some extent. However, these absorption lines are narrower than those of hydrogen (González Delgado et al., 2005). Therefore it is difficult to set adequate pseudocontinua at both sides of the lines to measure their fluxes. The reddening coefficients c(Hβ) were calculated from the measured Balmer decrements, F (λ)/F (Hβ). For consistency with the work by Hägele et al. (2008), we adopted the galactic
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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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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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