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

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44 3 • IFS of a GEHR in NGC 6946 Object Offset (α, δ) Exptime Grating GROT Spec. Range Dispersion Date (arcsec) (s) (Å) (Å pix −1 ) NGC 6946 0,0 3 × 500 V300 -75 3700-7000 3.2 09/07/2008 NGC 6946 1.56,0.78 3 × 500 V300 -75 3700-7000 3.2 09/07/2008 NGC 6946 1.56,-0.78 3 × 500 V300 -75 3700-7000 3.2 09/07/2008 NGC 6946 0,0 3 × 500 V300 -72 7000-10100 3.2 09/08/2008 NGC 6946 1.56,0.78 3 × 500 V300 -72 7000-10100 3.2 09/08/2008 NGC 6946 1.56,-0.78 3 × 500 V300 -72 7000-10100 3.2 09/08/2008 Table 3.2: Journal of observations and instrumental configuration. taken. These nine exposures were divided in 3 groups corresponding to different pointings. Each of these three pointings have a small offset in position from the other ones in order to perform a dithering mosaic. This allows to have a final mosaic with a filling factor of 1, so that there is no flux loss. This procedure was also followed in the case of the standard stars (see section 3.3.6). The observed spectrophotometric standard stars were BD +28 ◦ 4241 for the blue part of the spectrum (GROT=-75) and BD +17 ◦ 4708 for the red one (GROT=- 72). They were used to obtain the characteristic sensitivity function of the telescope and spectrograph for the spectral flux calibration. Calibration images were obtained following the science exposures and consisted of emission line lamps spectra (HgCdHe) or ARC exposures, and spectra of a continuum lamp needed for the wavelength calibration and to locate the spectra on the CCD, respectively. Figure 3.3 shows an Hα (not continuum-subtracted) of NGC 6946 showing the position of the PPak field at the NE arm of the galaxy. The center of the pointing is located at 4 ′ (6.85 kpc) from the center of the galaxy. 3.3 Data Reduction Integral Field Spectroscopy (IFS) is a technique for obtaining spectroscopic data of astronomical objects, in particular objects in crowded fields and extended objects like galaxies, planetary nebulae, star-forming regions, etc, collecting the spectra of many different regions of the object under identical instrumental and atmospheric conditions. In contrast to long-slit spectroscopy, IFS offers the opportunity to obtain three-dimensional (two spatial and one spectral dimension) information of an object from a single observation. To store three-dimensional information of a two-dimensional plane of a detector like a Charge-Coupled Device (CCD), it is necessary to discretize at least one dimension, done by the discretization of the focal surface in spatial elements. In most cases, the object is wider than the width of the slit of the long-slit spectrograph, loosing a significant amount of light. This is not the case of an Integral Field Unit (IFU) with lenslet arrays or fiber re-formatters combined with dithering methods in order to have a filling factor of one. 1 1 The difference among the major techniques of IFS reside, basically, in the fact that they just vary the way
3.3. Data Reduction 45 250 200 150 100 74.00′ ( 2.12 kpc) ¤DEC (arcsec) 50 0 −50 239.4′ (6.85 kpc) −100 −150 −200 −300 −250 −200 −150 −100 −50 0 50 100 150 £RA (arcsec) Figure 3.3: Hα image of NGC 6946 taken at the Kitt Peak National Observatory (KPNO) 2.1-meter telescope. The image has not been continuum-subtracted. The big hexagon shows the position of the PPak field and little ones the position of the six bundles of sky-fibers. North is up and East is towards the left-hand side. Another problem related with long-slit spectroscopy is the Differential Atmospheric Refraction (DAR), which is usually avoided observing near the Parallactic angle. IFS allows to correct this effect after the main reducing steps and before the data analysis. As mentioned before, the IFS method allows a determination of physical properties in two dimensions, but studies presenting two-dimensional maps of Hii regions (Maiz-Apellaniz et al., 1998) or Planetary Nebulae (PNe) (Rubin et al., 2002; Wesson and Liu, 2004) using different methods are not new. Nevertheless, due to the reasons mentioned before, IFS is a specific and powerful tool to perform maps analysis of physical properties. A considerable amount of time was invested in learning and developing reduction and analysis tools due to the complexity of the data from IFU instruments and the still in how the focal plane is segmented, and how the light is coupled into the spectrograph. A detailed discussion of all the different IFS techniques can be found in Allington-Smith and Content (1998).
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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
Page 13: CONTENTS iii B •Physical conditio
Page 16 and 17: vi LIST OF FIGURES 3.12 Example of
Page 19 and 20: List of Tables 1.1 Integrated prope
Page 21 and 22: Chapter 1 Introduction 1.1 Overview
Page 23 and 24: 1.1. Overview 3 Figure 1.1: Sample
Page 25 and 26: 1.1. Overview 5 These massive star
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Page 29: 1.2. Aims and structure of this wor
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94 3 • IFS of a GEHR in NGC 6946
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106 4 • Long-slit spectrophotomet
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Hδ 116 4 • Long-slit spectrophot
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Table 4.4 continued SDSS J1657 Knot
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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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