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

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38 2 • The star formation history of NGC 5471 region. In order to visualize this, we have selected four different areas in the CMD and proceeded to locate spatially the stars in these four boxes. Figure 2.11 displays the resulting distributions. The youngest and more massive stars (a) are clearly concentrated in the main star forming emission line knots, implying that massive stars form mainly in clusters. Only two stars are not directly associated with these knots, one of which belongs to an isochrone of 20 Myr. Panel (d) displays the distribution of intermediate mass stars (∼ 5−10 M ⊙ ) older than about 50 Myr; these stars are distributed mainly towards the halo, with only a few in the core of the region. Panels (b) and (c) show the distribution of intermediate mass stars (∼ 10 − 15 M ⊙ ), both those which are in the main sequence and those which have already evolved out of it. The distributions of stars in these two CMD boxes are clearly fairly uniform throughout the core of NGC 5471, with some of them distributed in the halo, a somewhat complementary spatial distribution to the older lower mass stars in the bottom-right panel. Because the stars in these two intermediate boxes are of the same mass but they are found in a range of evolutionary stages, this implies that star formation has proceeded more or less uniformly in the core for the last ∼ 20 − 50 Myr. From this analysis of the spatial distribution of the CMD, a clear picture emerges in which the star formation in the NGC 5471 complex has proceeded in a general spatiotemporal sequence from the halo inwards to the core. During the first epoch, ∼ 50−100 Myr ago, the star formation occurred mainly in the halo, then it moved inwards and occurred more or less uniformly in the core ∼ 20 − 50 Myr ago, although some of the star formation was also important in the halo, and finally the current ionizing star forming event is mostly concentrated in the singular bright clusters well located within the core. At the same time, we have seen that, both from the integrated photometric analysis and from the CMD, as the events moved inwards from the halo to the core the amount of mass of gas formed into stars seems to have increased. We note that the current event of ionizing clusters is apparently contained within a large bubble which defines the core of NGC 5471. This bubble, of projected size 400 × 550 pc, is clearly defined geometrically (cf. Figure 2.2) and kinematically (Munoz-Tunon et al., 1995), and is likely to have been produced by the stars that formed ∼ 20 Myr ago. There are other examples that seem to follow the general process of star formation that we have outlined here for NGC 5471. Walborn and Blades (1997) find a similar spatio-temporal distribution of stars in 30 Doradus, and Úbeda et al. (2007) also find an inwards sequence of star formation and a bubble for cluster I-A in NGC 4214.
Chapter 3 Integral Field Spectroscopy of Hii region complexes. The outer disk of NGC 6946 3.1 Introduction NGC 6946 is a relatively nearby, nearly face–on spiral galaxy with an exceptionally gas–rich disk which shows evidence for a high star formation rate (SFR) throughout (Degioia-Eastwood et al., 1984) and has been classified as having strong nuclear starburst activity (Elmegreen et al., 1998). The six historical supernova remnants recorded during the past century attest to this high star formation and justify the popular name “Fireworks Galaxy”. NGC 6946’s orientation and large angular size (D 25,B = 11. ′ 2) offers the prospect of studying the structure and star forming properties of the disk. NGC 6946 and its many supernova remnants have been the subject of numerous X–ray, optical and radio papers. At mm wavelengths the CO molecule, used as a tracer of the dominant molecular species, H 2 , has been observed by several authors (Ball et al., 1985; Casoli et al., 1990), showing that the CO distribution has a central density peak and barlike gas structure. Morphologically, NGC 6946 is a late-type SAB(rs)cd spiral galaxy (de Vaucouleurs et al., 1991), with several spiral arms and star-forming regions scattered throughout the disk, considerable extinction and a small nucleus. Its general properties are summarized in Table 3.1. K-band images reveal four prominent, not very symmetric arms (Regan and Vogel, 1995). 39
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Facultad de Ciencias Departamento d
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A Abigaíl, mi ut A mi familia, por
Page 8 and 9: 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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88 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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