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

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40 3 • IFS of a GEHR in NGC 6946 Property Value Type SAB(rs)cd a R.A. (J2000) 20 34 52.3 a Dec. (J2000) 60 09 14.2 a Distance 5.9 Mpc b D 25 × d 25 11. ′ 2 (16.6 kpc) ×10.0 (14.8 kpc) a V sys 47 ± 4 km s −1c m T 0 (B) 7.78a M T 0 (B) -20.92 L T 0 (B) 5.3×1010 L B⊙ B − V 0.4 a M/L (B) disk 1.2 ± 0.2 c 6.4 × 10 10 M c ⊙ M ∗ M HI M H2 Inclination Position angle Central metallicity Metal. Gradient SFR a RC3 (de Vaucouleurs et al., 1991) b Karachentsev et al. (2000) c Carignan et al. (1990) d Rogstad et al. (1973) e Tacconi and Young (1986) f Belley and Roy (1992) g Ferguson et al. (1998) 2.0 ± 0.1 × 10 10 M d ⊙ 1.2 ± 0.1 × 10 10 M e ⊙ 38 ± 5 c 240 ± 3 c 12 + log O/H = 9.36 f -0.089 dex kpc −1f 2 M ⊙ yr −1g Table 3.1: NGC 6946 general properties. Table adapted from Walsh et al. (2002) NGC 6946 appears in the ARP’s atlas, due to the “thick” optical arm in the NE, also seen in the deep Hα map presented by Ferguson et al. (1998). CO observations have identified NGC 6946 as having one of the most massive and extended molecular gas components observed in a nearby galaxy (Young et al., 1995). Atomic gas is also found throughout the disk, although it is found in highest concentrations in the spiral arms and appears less massive than the molecular component (Tacconi and Young, 1986). There is a nuclear starburst in the central 11 ′′ of NGC 6946 (Degioia-Eastwood, 1985). Several studies of the Hii regions have been made (Hodge, 1969b; Hodge and Kennicutt, 1983). The bright nucleus is characterized as an Hii region nucleus on the basis of the strength of [Oi]/Hα and [Sii]/Hα line ratios (Ho et al., 1997). The distance to NGC 6946 has been variously quoted to lie within the range 3.2-11 Mpc.
3.1. Introduction 41 Figure 3.1: Color composition image of NGC 6946 (credits: Volker Wendel). The box indicates the location of the GEHR, at about 4 ′ from the center of the galaxy. At the upper right corner it is shown a close-up of the region. North is up and East is towards the left-hand side. This uncertainty is partly because the galaxy is localted at a relatively low Galactic latitude (b = 12 ◦ ) and is subject to significant foreground extinction from our Galaxy, varying from A B = 1.48 (Schlegel et al., 1998) up to A B = 1.62 (Burstein and Heiles, 1984). The distance to NGC 6946 is listed as 5.5 Mpc in the Nearby Galaxies Catalogue (Tully, 1988), but a more recent value is 5.9 ± 0.4 Mpc (Karachentsev et al., 2000), based on blue supergiants. Here we use a distance of 5.9 Mpc to NGC 6946. Assuming this value, 1 ′′ in the sky corresponds to 28.6 pc. As mentioned before, NGC 6946 has a particularly extended disk of neutral hydrogen and is among our best examples of galaxies with extreme outer disk star formation. Figure 3.1 shows a color composition image of NGC 6946. From the core outward, the galaxy’s colors change from the yellowish light of old stars in the center to young blue star clusters and reddish star forming regions along the loose, fragmented spiral arms. The box indicates the location of a Giant Extragalactic Hii Region (GEHR) complex studied in this work, placed in the “thick” optical arm in the NE, at about 4 ′ from the center of the galaxy. This
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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
Page 11 and 12: Contents List of Figures List of Ta
Page 13: CONTENTS iii B •Physical conditio
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90 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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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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