TRACING ABUNDANCES IN GALAXIES WITH THE SPITZER ...

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II and Ib/c) supernovae (SNe) explosions. They produce the bulk of the oxygen, the principal element in the global abundance, as well as the bulk of other α- elements (such as argon, neon, and sulfur) which are formed by fusing together α particles (helium-4 nuclei, He +2 ) either in the core of the star or during the explosion (Matteucci, 2008). These supernova also produce other heavy elements through the r-process, the rapid capture of neutrons onto seed nuclei relative to the timescale of β decay (Woosley et al., 1994). Such massive stars have short lifetimes in the range of 1 to 10 Myr. Type Ia SNe caused by exploding white dwarfs in binary systems produce most (∼70%) of the iron and small amounts of other heavy elements (Matteucci & Greggio, 1986). Because the progenitors of these Type Ia SNe are low-intermediate mass stars, they have long lifetimes of several 10 Myr to over 10 Gyr. These low mass stars live longer than the massive stars which produce oxygen and other α- elements, and thus there is a delay between the iron and α-element enrichment of the ISM for a group of stars which formed at the same time. Thus the abundance ratio of α-elements to iron [α/Fe] can serve as a ‘cosmic clock’. Low and intermediate mass stars with masses in the range ∼0.8 to ∼8 M⊙ ignite helium in their core and dredge-up episodes occur which bring the processed material from the core to the surface. The stars then eject some of their material in stellar winds during the Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) phases (Iben & Renzini, 1983). Radiation from the central star ionizes this ejected material which then “lights up” during a planetary nebula (PN) phase before the star ends its life as a carbon-oxygen white dwarf. In this way the stars restore part of their processed and unprocessed material to the interstellar medium, enriching the interstellar medium in helium, carbon, nitrogen, and the heavy s-process elements which are made by the slow capture of neutrons onto 3
seed nuclei relative to the β decay timescale (Iben & Renzini, 1983). While each of these stars has much less mass and evolves more slowly than a massive star, the Galaxy contains many more of these low-intermediate mass stars, and they probably produce most of the nitrogen and carbon in the interstellar medium today (Chiappini et al., 2003), making carbon mainly as a primary element and making nitrogen mainly as a secondary element during hydrogen burning (in the CNO cycle). In summary, stars with masses (∼8 M⊙–100 M⊙) which explode as core collapse SNe make most of the α-elements (like oxygen, neon, sulfur, and argon) as well as heavy r-process elements on short timescales (1–10 Myr). Low–intermediate mass stars that end their lives as Type Ia SNe produce most of the iron and limited amounts of other heavy elements on long timescales (10 Myr to 10+ Gyr). The other low–intermediate mass stars produce helium, carbon, nitrogen and heavy s-process elements, releasing their material into the interstellar medium also on long timescales. The abundance ratio of an element released in to the interstellar medium on a short timescale to that of an element released on a long timescale serves as a cosmic clock, revealing the nature of the chemical evolution of a galaxy. 1.1.2 Formation and Evolution of the Galaxy Figure 1.1 shows a diagram of the different parts of the Milky Way. The Disk (including the Thin and Thick Disks) contains gas and stars. The Thin Disk contains most of the mass of the Disk and the young stars; the Thick Disk contains only a few percent of the total mass of the Disk and most of the old stars. The Bulge resides at the center of the Disk, and a spherical Outer Halo of stars surrounds the Disk and Bulge, with a spherical dark matter Halo extending out beyond the stellar Halo (Carroll & Ostlie, 1996). The Inner Halo of stars has a more squashed 4
Page 1 and 2: TRACING ABUNDANCES IN GALAXIES WITH
Page 3 and 4: TRACING ABUNDANCES IN GALAXIES WITH
Page 5 and 6: BIOGRAPHICAL SKETCH Shannon was bor
Page 7 and 8: ACKNOWLEDGEMENTS First and foremost
Page 9 and 10: thank my husband Ryan. The rest of
Page 11 and 12: 3 Chemical Abundances and Dust in P
Page 13 and 14: LIST OF FIGURES 1.1 Diagram of the
Page 15: ditionally we find that these nebul
Page 19 and 20: shape (Carollo et al., 2007). These
Page 21 and 22: Boltzmann velocity distribution cha
Page 23 and 24: etween recapture and photoionizatio
Page 25 and 26: a whole. Additionally, abundances f
Page 27 and 28: at the appropriate temperature and
Page 29 and 30: (a) 3.37 eV 1.40 eV 0.10 eV 0.04 eV
Page 31 and 32: (Iion), the radiative transition ra
Page 33 and 34: lines. For example, changing the ad
Page 35 and 36: Figure 1.4 Starburst99 synthetic sp
Page 37 and 38: Figure 1.5 Example of crystalline s
Page 39 and 40: H H H H H H H H H Anthanthrene C H
Page 41 and 42: year lifetime. Spitzer is in an Ear
Page 43 and 44: CHAPTER 2 THE SPITZER IRS INFRARED
Page 45 and 46: these elements than previous studie
Page 47 and 48: dust is seen in the spectrum. We se
Page 49 and 50: Figure 2.2 Close-ups of emission li
Page 51 and 52: 2.4 Optical and UV Data We compleme
Page 53 and 54: 2.5 Data Analysis Our goal is to ca
Page 55 and 56: 2.5.2 Electron Density We assume an
Page 57 and 58: Table 2.6 Electron temperatures ass
Page 59 and 60: O, N, and C. The helium ionic abund
Page 61 and 62: Barlow (1994) use UV lines for impo
Page 63 and 64: is a spherical nebula with a low ma
Page 65 and 66: CHAPTER 3 CHEMICAL ABUNDANCES AND D
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essential data on important ionizat
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are members of the Bulge, (Acker et
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Table 3.2 Properties of observed GB
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nod-averaged line fluxes. Uncertain
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Table 3.3 Multiplicative scaling fa
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Table 3.4 Observed infrared line fl
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3.5 Data Analysis 3.5.1 Abundances
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Table 3.6 Comparison of the derived
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from the most reliable line(s), and
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Table 3.7 Electron temperatures and
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Table 3.9 Ionic abundances Ion x a
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3.5.2 Crystalline Silicates Crystal
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argon, neon, and sulfur tend to be
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Figure 3.2 Continuum subtracted spe
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Figure 3.3 Profiles of PAH features
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mean argon and sulfur abundances ar
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of two smaller than that of Simpson
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towards the Galactic Center. On the
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Table 3.14 Parameters of linear fit
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models that show how a binary compa
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y an outer dense O-rich torus, indi
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CHAPTER 4 ABUNDANCES IN H II REGION
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expect their abundance ratio to rem
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We extract spectra processed throug
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Figure 4.2 IRS spectra of H II regi
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IRS slits from these WIRC observati
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S IV) we employ is equal to Te(O +2
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Figure 4.3 M51 H II region Ne III/N
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Figure 4.4 shows a plot of the (Ne
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James Webb Space Telescope (JWST);
Page 127 and 128:
Bernard-Salas, J. & Tielens, A. G.
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Edgar, R. G., Nordhaus, J., Blackma
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Hummer, D. G., Berrington, K. A., E
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Matsuura, M., Zijlstra, A. A., Mols
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Pradhan, A. K., Montenegro, M., Nah
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Vassiliadis, E. & Wood, P. R. 1993,
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TRACING ABUNDANCES IN GALAXIES WITH THE SPITZER ...

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